I just assembled a mini-ITX computer recently. It's amazing having the entire system on a 6x6 inch motherboard. A few inches deep for the CPU cooler. The NVMe SSD is inside the motherboard.

I do have a gigantic external GPU which almost doubles the size of the entire system, and because of that I also need a decently big power supply. But the entire system is literally just incredictlmotherboard + attached GPU + power supply.

Being able to fit it all into a NZXT H210 (still relatively big compared many other SFF cases) is great, especially for transporting it between college and home.

It was about 50% cheaper than buying an equivalently specced laptop. And any laptop with this performance would need to be really big and heavy to accommodate the cooling requirements (45 watt CPU, 220 watt GPU).