I’ve only ever modified files I’ve found online, never designed anything myself in Cad and I find plenty of real uses for my 3d printer. It probably paid for itself just printing organization bins and other things for the house. Just last week I bought some cheap shelves from IKEA clearance without any hardware, printed out some feet and now I have a new monitor stand. I regularly print accessories that I would otherwise have to pay extra for (like tripod mounting plates)

Plus there are some pretty amazing projects out there that get a lot cheaper if you have access to a printer. Personally I’ve printed a pair of astronomy binoculars https://www.analogsky.co/ and a custom mechanical keyboard fitted to my hand. https://ryanis.cool/cosmos/beta