I love that having a 3d printer means you can create custom parts when you need them. I wanted a set of leveling brackets for a router table insert. Sketched up something in Solid Edge, sent it to the printer and a few hours later I have what I need. Nothing complex but functional. Used PETG on this set.
My great-uncle never learned how to use a computer (well, other than the TRS-80 he got before he retired). He was pretty mechanical though. Even if he probably wouldn’t understand much about how it worked, he probably would’ve appreciated 3D printing if used for a car part or something!