To get new friends? Keep up to date with artists? Stan-wars? Everything?
I've had it since 2010 and basically only follow 20 people xD Only a few people I know IRL have Twitter, so I use it mostly to talk to them, but I want to follow more "fans" of artists and people who share the same interests as me.
Unlike a lot of other ATRLers I created my Twitter just for friends, random people, entertainment. It wasn't a "for my fave" thing or anything stan related. I got a Twitter for the same reason I got a Facebook.