I've bought two Minis as dev machines in the past. Portability was part of it. I also saved a bunch of money because I already had a full set of peripherals. Edit: Upgradable RAM and the ability to install a second drive was also great in retrospect, I wonder if the latter is still possible with the 2018 model.

And I'm not sure whether glossy Retina screens are really the best bang for the buck for developers. I often wish I had dual 1440p or a ginormous 21:9 screen when I'm dealing with complex projects.