I put mITX because it's the most fun to get a working system. Back in the day I was big on getting a cheap portable computer for lan parties and was really big on getting shuttle barebones and what the manufacturers were doing with their SSF selection. My home computers will always be ATX. Besides my need for drive bays, mATX doesn't lower my footprint so it doesn't really matter if the case is 2 feet tall or 5. So it certainly my primary case choice. But the satisfaction of getting a half way decent computer into something nearly the size of a shoe box has to be one of the greatest DYI feelings.
Then I got my Ncase M1. Then I got a fully functional, i7 system with 16GB of memory, SSD, storage drive, Bluray Burner, water cooling, all in a package that looks great and could be tossed into a backpack. It went from an ok solution to portable gaming, to a full blown system that is as good as any other in a miniature package. Even though I don't travel game nearly as much I think I will always want a system like that in the future. It's been a couple years and am thinking of turning it into a mini workstation. Either next year with a Zen+ or wait till 2019 and putting a possibly 12c system into it. But regardless as it is now it's my favorite system. More than my 3930k HAF X system when I built that, or my new Ryzen 7 1700 Define R5 one I built this year even if I don't use it nearly as much.