I leave mine on all day but shut it down completely when I go to bed, unless I am downloading something. I've never liked "sleep mode" as I've always had trouble"waking" it up. Sometimes I leave my older computer on over night though but usually just for one night (for my own weird reason).
This is pretty much what I do. Another reason I shut mine down completely before I go to bed is in case there is a power outage (which we have far too many of here - they have ultra-sensitive settings for the power lines due to fire danger, and this has made things even worse during the months of June through October).