I never quite "got" twitter, it was never fun for me to participate on. It's telling / disturbing that folks had such trust in random accounts ...
Scientists/Researchers
Journalists
Activists
Politicians
Subject Matter Experts (for the fields I am interested in)
There were (when I was using it) a large number of "troll" accounts, and bots, but it was normally easy to distinguish the wheat from the chaff
You could also engage in meaningful conversations with complete strangers - because, like Usenet, the rules for debate were widely adopted, and transgression results in shunning (something that I rarely see beyond twitter to be honest)