It's only a distraction if my crappy laptop starts to freeze because it can't handle too many things open. It has happened to me a few times when I play StockPoker, and have Twitch open on the same laptop/device.
When it's working, I think I play better because I want to last longer, and do good while the game is being streamed.
I think it helps me too.. The streamers are hilarious and their commentary teaches you stuff. Without it, my mind wanders way more. It's weird how distraction can sometimes improve concentration, right?