Boxed sets make a lot of sense for adventures. They allow you to give maps and handouts to players, while keeping the DM material disarticulated in a way that is possibly helpful for the DM. Of course, sets vary in terms of execution on this front.
In terms of settings, though I listed to the two planescape boxed sets as my favorites, I'm not sure it was the best use of the format. A lot of the material was repeated across the player's and dm's guides, and the poster maps, while pretty, were planar and thus abstract. Those boxed sets would have worked just as well as dm-facing gazetteers. At the time I remember it was thought that the boxed sets allowed TSR to charge more money, though I think a lot of them were overly costly to print and put together.