space - you have to have at least 1 dedicated desk for your desktop.

mobility - You can do your work in places other you workplaces/home. Change of scenery/environment is trivial. even inside your own house, you can work from your own bedroom, kitchen, lounge, garden, wherever you want.

Your last point is baffling, really. Just treat it like any PC. If you dont want to use the screen/keyboard/trackpad just connect what you want to the laptop.

Actually I dont see the point of mini PC. Theyre just desktop that you can lug without monitor and any input devices. What's the point of spending huge sums of money on a mini PC that performs 1/2.9 compared to its PC equivalent?