Just out of an abundance of caution, I leave as much "off" as I can. Currently I don't even have BT turned on this laptop. I don't know of any BT exploit (not saying they don't exist, just that I don't know .... ) but I figure that if my habit is to be overly cautious, and turn on services only when reminded by a dialogue box telling me it can't do something, then I don't need to worry should an exploit be developed.