A full tower case is indicated if you plan to use more drives than a mid tower case has locations for, in some cases when custom loop cooling doesn't offer sufficient room, in closed loop cooling configurations when two 360mm radiators need to be used independently for the CPU and GPU, or when you just want it fricken big, so there's tons of extra space to work with. It's also sometimes necessary if you want to use 280mm liquid coolers rather than 240mm versions. There are mid tower cases that support 280 and 360mm coolers, and I've listed a couple of them above. You just have to know what size cooling you want to use and check it against the case specifications.
Most manufacturers and vendors pages list what size radiators, and WHERE, they support, as well as the max CPU cooler height if you go with air and what length graphics cards they support. Also it's sometimes necessary for a full tower case if you use an extremely large power supply that's too long or wide for a mid tower case, which is pretty uncommon these days, or if you need a LOT of 5.25 drive bays on the front of the computer.