I feel it clutters up my page and is needlessly redundant. I leave the status option on though, because that's nice if you want to say something but don't feel like making a journal about it. Nice for updates and things like that.
I usually show my activity because 1. I'm always logged in but not always actually online so it might give people an idea of if I'm actually here doing stuff or not and 2. I feel like I don't have any reason to hide what I'm doing. :'D