Inspired by this post, I'm wondering if cathedrals served any practical purpose for the community which helped construct it aside from mass. If not, what was the benefit to the community of having these large, expensive, structures. I'm mainly wondering about the middle-ages but open to any time period in which you may have expertise.
There actually are a few ways that churches functioned aside from housing worshipers for Mass, but these are, of course, directly related to the church’s larger spiritual aims which took precedence in the Middle Ages. I can’t demonstrate every way that the space of the church was used at this time but I can give a few specific examples. Incidentally, both of these also relate to how churches raised funds for their own repairs and construction.
Perhaps one of the more prominent practices that became widespread during the range of dates you specified was the practice of pilgrimage in which devout churchgoers would visit the shrine of a saint or holy person—this could consist of their physical remains or some object that they had touched worn, etc—and pray in the presence of these objects so that they could for example, be forgiven for their sins, or be granted a miracle. Over time, some of these objects gained a reputation for being miraculous and thus attracted the attention of more pilgrims. This led not only changes to in the physical structure of the church itself but also alternative uses for its space. A well-known example of this is the Church of Santiago de Compostela, completed in 1211, and built to house the relics of St. James. As it was made for the benefit of pilgrims rather than local parishioners, this church had a prominent ambulatory with small chapels around it so that visitors could venerate the relics without interrupting mass (floor plan). They could enter through the transept (side-entrance), explore the space of the church, and visit the relics located around the perimeter without disturbing the activities taking place in the nave and high altar. This practice became fairly widespread and even became the impetus for a sort of economy with hostels, pilgrimage churches and other forms of proto-tourist infrastructure popping up along major pilgrimage routes.
Another example of the popularity of pilgrimage can be seen with Chartres Cathedral [(floorplan)] (https://upload.wikimedia.org/wikipedia/commons/b/b1/Plan.cathedrale.Chartres.png) [(exterior)] (https://upload.wikimedia.org/wikipedia/commons/2/21/Chartres_Cathedral_000.JPG) and, incidentally, it is also an interesting example of how major construction projects came to be funded. The relic it contained was purported to be a shift worn by the Virgin as she gave birth to Christ. This particular relic had healing powers attributed to it which made Chartres a major pilgrimage destination. In fact, during its rebuilding in 1145, wagonloads of donors arrived with food and construction materials to sustain the builders and in return were allowed to see the relics (Freeman 115). In yet another creative way of raising funds (in addition to those from bishops, church officials, and aristocratic patrons, of course), the churchmen at this cathedral played on the public’s particular interest in this relic and sent it on tour as a way to generate money for the construction of this church. This practice positions pilgrimage as a major factor in a sort of medieval proto-tourism and an influence on the economy of Europe.
Another more peripheral way that the church functioned during the medieval era was as the base for larger monastic communities. Although here the space was still used in largely the same way, it did spur the construction of supporting communities of monks whose interactions with the surrounding community broadened the ways that individuals could interact with the church. For example, if you look at the [St. Gall plan] (http://www.stgallplan.org/en/index_plan.html), a plan of what an ideal monastic space should look like, you can see that while the church forms the bulk of the architectural space, it also contained a hostel, guesthouse, school, and infirmary. While this particular plan was never executed, (it represented an ideal layout of space) it does show how monastic communities provided public services that could be later associated with the church.
Sources consulted:
Charles Freeman, Holy Bones, Holy Dust: How Relics Shaped the History of Medieval Europe
Carolingian Culture at Reichenau & St. Gall: http://www.stgallplan.org/index.html
For clarification, is there a specific time period or geographical area in which you are specifically interested?
Let me start of by saying that I'm probably not the most qualified person here to answer your question. But i really like the question and i think it deserves an answer. I'm not a church or social historian. I'm a medieval historian that focusses on the northern low countries mainly in the period between 1100 and 1500. This means that first of all my answer is going to mainly be true for that period and that area, when i give examples that aren't found in the norther low countries i will specifically mention place names. It also means that i wont be able to provide a proper source for most of this, since it is quite general information that i picked up at lectures or symposiums. If anybody would like a source on something i said, please let me know and ill try and find it somewhere.
If i may, i would like to change the question a little bit. A cathedral isn't a big or ornate church, it is the seat of a bishop. Not every cathedral was big and ornate and not every big and ornate church was a cathedral. I would like to answer the question for any big ornate urban church in the high till low middle ages. One of the reasons for this change is that my area of expertise, the norther low countries, only had one cathedral in Utrecht but many more big urban churches.
So the question would be. What were the practical functions of big urban churches between 1100 and 1500? There are a couple of uses and functions big urban churches would have during the middle ages and i think the following 6 points are the most important out of all of them. But this is by no means an exhaustive overview.
Prestige
In the middle ages being part of an urban community meant something to the members. Cities in the northern low countries were still real communities. The norther low countries had many small till medium sized cities. The biggest city being Utrecht, having around 10.000 inhabitant, most cities having around 3000 people living in them. The people living in those cities were burghers of these cities and as such had certain rights and privileges within the medieval world. They were proud of these privileges and freedoms and as such the city was often the highest unit of government they felt a real loyalty to. For the burghers having a big church that would rival a cathedral even though there was no bishop was a point of pride. Having a big altar stone made of foreign rock, a full time choir that fills the church with song or the highest tower of the region was a real concern and something they were prepared to spend a lot of money on. If a rival trading town would build a church more ornate then the one of their own community, the civil leadership would sometimes attempt to raise money to one up them.
Tourism
That's right, medieval tourism. Well maybe it would be more accurate to call it pilgrimage. Anybody who has read the Canterbury tales is probably familiar with the concept of tourism in the middle ages. Some people would have been moved by spirituality or the need to heal a certain ailment other just wanted to see the sights and drink beer. Having a big ornate church with relics could help attracting pilgrims to the city who would in turn spend money on food, drink, bed and souvenirs. Some extreme examples of cities that had a real tourism industry would be Canterbury or Santiago de Compostela. But every city had their regional legends and saints. (This was before the papacy regulated sainthood) Even relatively small towns could try and attract pilgrims. Most wouldn't be on a European scale, but having a famous relic or miracle would even attract pilgrims to small town or village churches on a regional scale.
Capittel/Collegiate churches
This is were we venture in a little bit of less known territory. By the late middle ages every city of some importance would have had at least one church with a capittel. Utrecht besides their cathedral had 5 churches that had a capittel staffed by cannons. Being a canon was a particular lucrative ecclesiastical position often staffed by university educated career clerics and the low nobility. Having some level of learnedness was often required and this was a way for the patrons of the church may they be nobility or as was often the case civil to bind influential or skilled clerics to them. The position of canon was particularly lucrative because they were more often then not connected to a prebend. A prebend is a collection of land or other goods that would produce the income of the canon. This college of cannons were headed by a deacon or provost (sometimes both) who often head a very substantial prebend. This meant that big churches were often also administration centers for big estates and sometimes even had lordly rights over villages or areas. In cities with a bishop the canons would also be officially responsible for choosing the new bishop, so they would have to be bribed by anyone or their patron aspiring to that position.
Schools
Capittel churches often had schools. Before there was the university there was the capittel school and in western Europe many Universities have their roots in capittel schools. The professors were often canons, giving out lucrative prebends with these canonships was a way to bind professors to the school or attract more learned and famous ones. While classes and lectures would often be held outside of the church itself, these professors and students were bound to the church and therefor to the city. While especially in the late middle ages when Universities and secular latin schools started to gain ground, in the high middle ages these were some of the most important cultural and knowledge centers of Europe. (Along with a handful of really important monasteries) Having a capittel church with lucrative prebends would have been a way for a town to attract both professors and students. While students would often bring trouble, they would also bring money.
Lay involvement
From around 1300 onward lay involvement in churches would flourish in the northern low countries. Lay brotherhoods were founded for people wishing to get spiritually involved, but not able or willing to take the vows. Guilds also played a big part spiritual revival of sorts in lay culture. Both these lay brotherhoods and guilds payed to have chapels build inside or next to big churches. They would furnish and decorate these chapels, bury their important death in them and pay for a chaplain to perform services in these chapels. These chapels were more then just spiritual places for these brotherhoods and guilds. From these brotherhoods in the low countries would form so called "rederijkerskamers", these were brotherhoods of lay people that were amateur writers, musicians and stage performance. These were the first real clubs for amateur artists in the low countries and the civil expression of culture that would displace the courtly literature that was popular during the high middle ages. These clubs gave the burghers a cultural voice and are regarded as being very important by scholars of Dutch language literature, these clubs were really just lay brotherhoods based out of churches.
Social center
From the smallest parish church till the biggest urban cathedral. The church was a place for the community to gather. Churches were not just open during mass or sermon, but were often open during the day. People would come in to pray, listen to the choir, look at art or in the northern low countries even read sermons pinned to the wall or pillars. But there weren't just spiritual reasons to visit the church. Often merchants would conclude business deals in the church. It was a public place, often very central and maybe even more important; who would try and cheat or lie about a deal in a church? But people could also come in and converse. Urban churches were full of life, not only during mass. They were often quite busy the entire day. There were priests, chaplains, canons, students, singers, musicians, merchants, guild members, lay brothers, normal townsfolk and often even cats and dogs in the church.
I hope this answers most of your questions about how these big ornate buildings were practically used in day to day life. If you want i can tell you a little bit about how the medieval theologians felt about the buildings beings so ornate if you're interested, but i would type that up some other time.
Some sources: (I'm sorry that i cant do better)
About the role of capittel churches in medieval education: Charles Homer Haskings, The Renaissance of the Twelfth Century (Cambridge 1927).
About capittels in the northern low countries general: A.J van den Hoven van Genderen, De heren van de kerk : de kanunniken van Oudmunster te Utrecht in de late middeleeuwen (Zuthpen 1997).
About medieval society: W. Blockmans and P. Hoppenbrouwers, Introduction to Medieval Europe, 300-1500 (Routledge 2007).
