Right Jon, say you were trying to sell/distribute folk music online. You would want to research the folk music traffic already online to find out how to bring them to your site. You would want to know how to get your website to come up to the top of the first page of a Google or Yahoo search for "folk music vendors" or some such keyword search. In order to see that happen though, you do need to know about your competition, and know about your natural allies online. Competition being other ecommerce sites dealing in folk music sales, and allies being places on the web where people go most often to learn about and/or discuss the type of folk music you sell. You will want to study the sites which get the most traffic, but also the sites with the highest sales, even if they aren't also the sites with the highest traffic.

That sort of stuff.