For desktop users, size of the machine is not nearly as important as raw. computational. power. The iMac was good in its time but that time was half a decade ago. The Mac Pro was supposed to be the revolution for Mac desktops, but they neglected it for too long. And since you can't upgrade it yourself that shiny new Mac depreciates exponentially and even more so when software updates bog down resources further.
Support for specific combinations of hardware is near the flawless breaking point where just about anyone could follow the guides to put together a machine that will run MacOS using near top of the line hardware. Being able to dual boot Mac and Windows, so that I can be productive and game on a high end graphics card - and not locked down in expandability is unparalleled.