When I had mine off it's mainly to have some sort of 'privacy', since I will admit that I was ashamed of seeing the amount of time online that I'd spend on here. Now it's just out in the open, though I've contemplated on shutting it off again.
I can't speak for everyone, but I think it does give some privacy for them since others would be curious of them being online and how much time they seem to spend with it. -shrugs-