I think people who are into crafts. They have all of these yarns, construction papers, various tools and stuff. All so that they can say that they have all of these projects in mind that they want to do. But they never do them so they get more crafting stuff and it just eats away storage until their place is practically consumed by it.
3d printing, if you start it’s a wormhole, where you end up wanting more and more different types of printers, print a lot of useless crap, have a lot of filament lying around, and spare parts. Not as space consuming as automotive or woodwork etc but if you live in a small apartment without a dedicated room for hobbies it can get pretty crazy.