Mostly, I like to Vent as well (though I'd rather Teamspeak, but still ...). A few days ago, I did a Yag loop with some people from Rogue Angels. It was all silent, even in Cavern (on Mitra, there were people who thought it outright impossible to do emotions without someone calling them out loud) and it worked. Still I was glad when they invited me to their Vent server. They turned out to be very nice people and they were patient with me, even though I had some troubles setting up the whole Vent-thing and was struggeling with the english language.
So, for me, the reasons to Vent/TS are mainly a social thing, like Boesch already said.