I can't speak for economic in particular, but comparative studies really helped with my graduate historiography article. My topic was the Irish Famine, and the article that really glued my conclusion together was Armatya Sen's "Poverty and Famines," which was a comparative piece that placed the Irish famine within the larger context of famines and the economy in the British Empire. Comparative articles like this can expand the scope of studies on whatever topic drastically. Edit (needed to read your question again): by expanding the famine into a more global context, historians were able to ask questions that couldn't exist before, such as global British colonial policy regarding food shortages or British economic thought on underdeveloped societies.

Comparative analysis can be quite valuable when the writer seeks to demonstrate the ways in which one or two variables can change the development of otherwise materially similar groups or people. Comparative studies can also be quite useful for opening angles of attack for future study.

In your question, you mention the development of trade. Good place for some comparative work in that there are myriad societies that share a very similar past but have gone off in different directions.

For example, consider two fictitious peoples living near each other. Millennia ago, these peoples were, from a macro perspective, materially the same. Today however, one is more insular than the other. You seek to know why.

As you do your research into the history of these peoples, you discover that at some point in the past, an event occurred among people "A" that made them scared of dealing with foreigners. This event did not happen to people "B." Today, centuries later, we see that the long-term effects of this event include the tendency of people "A" to be much more suspicious in dealing with foreigners, causing the insularity. People "B" on the other hand, are deeply engaged in trade with foreign nations/peoples.

While of course there can be untold numbers of other causes for the eventual differences, if the evidence is strong enough that the two societies shared enough other mutual circumstance during their respective histories, an argument can be made that this event was a turning point, a major bend in the road for people "A."

Remember that when you do a comparative project, you are of necessity obviating a multitude of factors to focus on the one or two things that you feel caused whatever difference you feel is important. In the example above, this important event may have been one of a few similar, but in your opinion, less important events that people "A" endured. Perhaps people "A" also endured many other, dissimilar events that you feel did not materially contribute to their development. Unless you're writing a book-length essay, you'll have to narrow your focus, quickly.

FWIW, when I was in grad school, the comparative paper was the one my cohort dreaded the most. Comparative work is difficult to do well, and more difficult to do in a length-limited project. To balance the obviation of less-relevant stuff with the need to present an effective study is no small task. Think in terms of two decks of cards. Each deck is a nearly fully-developed project on one side of the comparison. You now shuffle them together and weed out the stuff you no longer need. Daunting, especially for student-level work. Some can pull it off much better than others.