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”.

Source: Self

Warhammer.

Hobby electronics?

Need a small part? Better buy 10 in case you break one and because it’s only marginally more expensive than getting one. Now repeat for every project you do

Oh man, woodworking is pretty bad. Tools galore, scrap wood everywhere, and half-finished projects all over the garage.

Any “retro” collection. Old video games, for instance. In many cases, the barrier to entry is sky high, because there are very few old consoles or games on the market; The collectors have bought all of them, and are never planning on selling.

Collecting stuff is basically the ultimate hoarder hobby.

I would actually love to know what hobbies don’t have some sort of hoarding aspect! I’m trying to think on it and I can’t come up with any at the moment.

I’m sure one of you can help me?

Model Railroading.

It’s not the worst, but it requires all the key ingredients - you need to own a home large enough to have a ‘spare’ room, which means you’ve got disposable income. And displaying the trains is almost as much fun as running them, so you end building shelves and shelves, which then sprawl out to the rest of the house. Only to realize you’re missing the ‘key’ one from that set, got to go find that, obviously.

And then of course you can’t throw away the boxes, because that would lower the resale value, so you need to rent a second storage unit. Not that you would ever sell them of course. But your kids will be sitting on a goldmine!

And that’s just the collection portion. It’s a crafty hobby, from making scenery & waterfalls & little trees all the way to the special paints to make the engines look aged. That will need a room as well.

And now that we’ve got the train shelves in the kitchen, you know, I could put a food themed railroad on the table there. Yes I already have the desert themed one in the train room and the prairie themed one in the living room and the snow theme layout in the hallway, but I don’t have a silly one. No of course the Halloween theme one doesn’t count.

Cars because they are so big, and ugly when in disrepair. Small scale hoarding is a small scale problem.

Backpacking. I have a big plastic bin filled with equipment that I decided to go another direction with.

But makers are the kings of hobby hoarding, just look at Adam Savage. He has parts for things he hasn’t even thought of building. He has a plethora of tools that overlap entirely just because the set of tools is closer to a given work aspect. Walls of bins with various degrees of filled because he bought 100 of something a decade ago that may have a future use.

Is this a place to cast shade or self reflect? In the former experimental scientist. They have closets of oscilliscopes, vacuum pumps, cryostats. Enough to furnish 3 or more labs. They always say they’ll use it, but the pile only gets bigger.

For me, I have the opposite problen in general. I throw everything away and end up buying or making new shit. Worst is probably code. Fuck making a repo. This is a one off. I can write the same code 3 times before I keep it, but I like to say that is what makes me a decent programmer. And I’ll keep telling myself that until I die.

Cycling can get bad. Some dudes have a garage full of $20k of bikes.

I am on the low end of the bike hoarding spectrum. I have two very modestly priced bikes (one road, one fat) and a 20” box of parts and accessories. You could count the 4 water bottles in the cupboard, 4 bike shorts in the drawer, and 6 bike jerseys in the closet as well. 2 pairs of bike shoes, a hook of tires and tubes in the garage, oh god never mind I have it bad.

Junko pop

antique airplane restoration. So many parts, so many unreplaceable parts, soo many tools, soo many large parts as well.

I know people are giving some very good examples, but a pet that can easily turn into a hoarding hobby is hamsters. You get one, get super attached, and then three years later whoopsie doodle, the living room is filled floor to ceiling with cages for all twelve of your little dudes.

This is just due to how much space the little guys need. In the wild hamsters will viciously defend miles of land, so bigger cages are always better. As a general rule, an ideal cage should have 900 sq inches of space and be at least 2 feet deep to allow several inches of bedding. So, one little dude will take up at least 12.5 cubic feet of your living room, or .07 cubic smoots for our friends across the pond. This adds up fast, and it can be easy to get in over your head because each individual little dude requires so little cage cleaning per month.