I use them mostly for RPGs and occasional short stories.

I'm just doing it for fun mostly, but I'm mostly a conlanger so it's also in large part just to be able to give some extra flavour to my conlangs based on the culture, history, etc. of the people who speak them.

Doing it because I'd like to write a story some day. But tbh it's also become a way to escape and stretch my "creative muscles" so that's nice

Mostly just for fun but also for my Savage Worlds campaigns. I hope to write something in it at some point.

I'd like to one day animate some of the history / lore.

Sort of the same for me. The world I make was mainly used in writing campaigns between me and a close friend of mine, we actually intended to write books together with the characters and elements we had, but long story short that isn't an option anymore.

Nowadays I'm just trying to flesh things out and get everything together in a neat and concise manner, which is what my own wiki project is for, alongside a set of short stories to accompany it, with intentions of having it be all under a CC BY free use sorta field so anyone can do whatever with what's there, though that's it's own topic for another time.

Since this community is also interesting for game development, I've included it in my list of gamedev-related communities.

That is also how I'll be using most of the worlds I come up with.

I'm mostly just doing it for fun, but I might one day make a comic or write a book or something set in it. I've considered using it for TTRPGs, but it's too different from D&D and Pathfinder's default settings to really be compatible with the rules.

I gained an interest in DND 5E some time ago and I didn't have anyone to play with, but I read the PHB and DM guide cover to cover and decided to use that time building a homebrew setting, so I made a map and started writing some history!