The Topical Studies on this site are longform series covering various topics in depth, in the manner of reference books. Their primary purpose is to flesh out areas of particular importance in a systematic way. Some of the Topical Studies are focused more on doctrine and theology, and some are focused more on application and implementation, but of course the lines are always somewhat blurry.
In many cases, topical studies are an aggregation of shorter pages from the pages section, along with additional content to glue things together. One might ask — why include the actual content of these pages rather than just including links to the pages? The main answer is because it makes uninterrupted reading possible, without having to constantly be juggling tabs and keeping track of where you are in multiple documents. It also makes these studies more useful when they are printed out, which some folks like to do. Links don’t work on paper!