I'll give you an example from my life. I got a set of cheap LED lights for a closet. They come with a little remote control to turn them on, but I didn't have a good place to put the remote control, so I made a little wall holster that's sized exactly to hold the little remote.
I also got one of those SimpliSafe home security systems. It came with a door sensor, but the sensor didn't quite fit our door frame. So I printed a tiny piece whose dimensions exactly matched the SimpliSafe and my door frame, so it allows the parts to meet up but doesn't look weird.
Of course, 99% of what I print is useless stuff that looked neat on Printables, but sometimes I make stuff that actually serves a purpose!
I also got one of those SimpliSafe home security systems. It came with a door sensor, but the sensor didn't quite fit our door frame. So I printed a tiny piece whose dimensions exactly matched the SimpliSafe and my door frame, so it allows the parts to meet up but doesn't look weird.
Of course, 99% of what I print is useless stuff that looked neat on Printables, but sometimes I make stuff that actually serves a purpose!