I agree, there's pretty limited usefulness to keep it enabled on a desktop. Unless you're at risk of someone walking off with it, like your desktop is in a fairly public area, or you live in an area where robberies/burglaries are not rare, I don't know that there's much value in it. You also have to think about what data you're realistically keeping on your PC. Is it something that if that were to become public information, would that be a problem?
Like, if you have pictures of yourself in blackface or nudes or something, maybe think about it... But if you're just using your PC to play games and browse the web, it's probably not very important to encrypt it. Even if someone takes it and looks through all your data, they probably won't find anything of value (to someone else) beyond whatever money they can get for the hardware.
It's a very personal choice, and with higher risk devices like laptops, I would say, just turn on the FDE, back up the recovery keys and forget about it. Desktops, meh. Up to you.