Collecting a set lets you turn it into a badge, which is a thing you can show off on your profile. Whenever you craft a badge you get an emote, a profile background, and some XP. The emotes and backgrounds are buyable with steam points, though you need to own the game iirc. The XP goes towards your steam level. Levels are just a little cosmetic thing for your profile/mini profile, but going up in levels give you more friend slots and more showcase slots for your profile if you're into that. If you don't care about any of this, then selling them is pretty much the only thing you can do with them.
Collecting a set lets you turn it into a badge, which is a thing you can show off on your profile. Whenever you craft a badge you get an emote, a profile background, and some XP. The emotes and backgrounds are buyable with steam points, though you need to own the game iirc. The XP goes towards your steam level. Levels are just a little cosmetic thing for your profile/mini profile, but going up in levels give you more friend slots and more showcase slots for your profile if you're into that. If you don't care about any of this, then selling them is pretty much the only thing you can do with them.