It's a category for discussing "deep dives" (when a researcher follows an idea, trend, or phenomenon down a rabbit hole, trawling for various kinds of information in the process) and "case studies" (an in-depth examination of a particular phenomenon in its original context). They're a great place to start the research process when there isn't much (if any) groundwork done on the specific topic you're interested in, and can serve as original research worth citing in and of itself.
Here's some examples which I've moved into the category:
Go ahead and try adding to the category or one of the threads above!