Please don't. I would avoid certain stream if I knew they were told that I've joined/left because I do that quite frequently without saying anything and don't want to come across as an asshole.
I don't know about other streamers, but I, for one, expect people to hang out for about 5-15 minutes. I do a coding stream, so it's bound to get boring :-) I'm always amazed when people hang out for the whole stream. People are busy and it's wonderful if they just pop by to see what's going on. At least in my stream, I'm always very happy to see someone say, "Hello. Just stopping by. Can't stay!" It's incredibly gratifying.
