I have a B+ mounted insideat the top of a tower speaker, plugged into a little amp when on it connects to home network. Volumio is running. Have a Pi Zero W inside an old tank model to hook up to TV don't use it much anymore but it is running Kodi.
There are so many things you could do with a Raspberry Pi, even more with a RPi4 since it has more computing power.
The two most adequate uses (for its computing power) I believe are gaming and movies.
For gaming you could install Retropie and emulate any kind of game (i.e. PSX, Nintendo Wii, Gameboy, N64...).
For movies you could install LibreELEC.
Just gave a guy at work a Lodge Iron skillet ain't used in years, and am giving him a 7 level Dehydrator, last time I used it just ended up making jerky for the dogs. Just found 3 boxes with Motherboards. I Asus Black Pearl, Pentium 3. (Named before the pirate movies) I Gigabyte and 1 Tyan Both AMD the last 2 of which were still new and unused. I am a pack rat, but becoming a pack mouse.