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.
My first answer would have been retro game collecting, but that's already been discussed, so I'll posit custom PC building. That's a hobby rife with keeping spare parts "just in case".
Oh man, the car parts one take up so much space too.
Do I need three exhausts for my WRX? Nope, but I keep banging them up off reading.
3 engine blocks, all needing some form of rebuilding. Mostly just new bearings. Or an entire extra wire harness because in the last rebuild it was just easier to buy a new one.
All my old shocks and springs after I replaced them with outback gear.
And that's just what fits on the car. I've got big brake kits for cars I don't even own! But they're like $2k if I can ever find a buyer.
You laugh and you joke but I stumbled into a PS2 original, the fat one, with a network adapter so you can slot a hard drive in. I went into my spare parts and pulled out an old IDE hard drive, as the PS2 was before the spread of SATA (I think even before SATA was announced) and it popped right in and guess who doesn't have to worry about discs
but it is a double edged sword, lol. now that i have proved to myself that those cables really will come in handy one day, i am forever stuck with a slowly growing stash of cables!