It's a little bit of a complex question, but the short answer was that the railways were useful to ordinary people in India.

First, it's important to understand how the railways were financed. Although they were originally built and constructed by private companies (the colonial government would later play a more prominent role in this) it was hard to get private capital to commit to such big projects, so the government offered them various types of subsidies. This made a lot of sense to the colonial government because they wanted to get better access to sell British manufactures to Indians, and better access to agricultural goods from India. But from the perspective of India it might have been better to subsidize investment in education and irrigation. Moreover, everything except for the unskilled labor was shipped from the UK, and the engineers conductors and everyone else was from the UK late until the 1930s. The benefits of constructing the railways flowed to the British.

As far as the question itself is concerned, the rail lines were constructed to connect the main export producing regions. The main exports were cotton, jute, indigo and cotton and those regions were connected. However, I'd be careful not to make Indian interests and British interests to be two totally separate things. While tea was mostly produced on British owned plantations, cotton, food crops, and oilseeds most of India's other export commodities were produced by small farmers. The expansion of the rail lines allowed these farmers to get their crops to market much faster. Moreover, the rails connected major metropolitan areas to their hinterlands. Most of Indian wholesale and retail trade was controlled by other Indians, so the profits of all the expanded trade largely stayed in Indian hands.

Of course, the expansion of the railways wasn't good for everyone. The expansion of the railways meant that manufactured goods could flood India. Handicrafts industries and artisans near the rail lines, because they reduced transportation costs. Finally, the rail lines weren't built to expedite global trade, to get farm goods to ports and British manufactured goods in. It wasn't designed for people, and had limited use in the transport of people. It also didn't serve the poorest regions of India, and wasn't used nearly well enough during the various famines.

So when it comes to the question of were the railroads good for India, the answer is complicated. My gut feeling is that they did more good than bad, based upon this paper. The econometrics of it are quite complicated, but the key thing is this. The regions where railroads were built, after you take everything else into account, are a lot richer than the areas where they were not built. This to me suggests that ordinary Indians benefited from them both in colonial times and today.

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India was a bit of a unique case in the British Empire for a variety of reasons, but in regards to its infrastructure India decisively benefited far more than other British colonies. As a general practice the British did not typically construct extensive railways throughout their colonies. Most colonies were sparsely populated with only a select few ports and centers of commerce which meant that, from the British perspective, it was not worth investing in railways as a form of public transport. As such most British colonies only had a few railways designed for British commerce and administration and were constructed and designed with little to no input from the natives. So the rails made in, say Africa, were not made with the native population in mind and the natives had no education or training on the construction and use of railways. So without the know-how of rail operations and more importantly lacking the education and knowledge/technology transfer most post colonial countries were left with limited,outdated railways and little in the way of resources available to allow them to improve the railways.

India however was different. Unlike Africa, India had several major centers of population, trade, and commerce, which meant that it would be beneficial to construct far more extensive railways. Thanks to the more extensive railways, trains were far more available for use to the average Indian and could be utilized by the natives for their own (albeit limited) economic gain. Even more importantly, due to the sheer scale of the rail construction taking place Britain could not rely solely on European Engineers to design and construct the whole system. Instead the British began training and utilizing Indian engineers to help with the railroads. This led to India's railways having, in places, a very unique mixture of European and Asian style engineering. More importantly though, it educated hundreds of native Indians on the know-hows of steam engines, railways, and western engineering. This is largely what allowed India to easily continue expanding its railways after de-colonization and largely why India to this day is famous for its grand railroads. So basically India did, in a sense, benefit from the colonial infrastructure but it is the exception, not the rule as most colonies did not.

The primary source of this information is a book entitled "Technology and the Raj", specifically the two articles included in the book "Colonial and Neo-Colonial Transfers of Technology" by Ian Inkster and "The Building of India's Railways" by Ian Derbyshire. It is, of course, debatable as to what extent the railroads were beneficial to the average Indian but overall it seems that western technology was transferred far more efficiently and was more beneficent for natives in India than in most colonies.