I too leave mine on, but to be honest I don't know why as each night, before I go to bed I always have at least 30% left. Might take it off for a few days to see if I like the way it looks without it on
I leave mine off now. When I first got the phone I was obsessed with my battery life compared to others. Now I just plug it in when my battery goes yellow or when I turn in for the night; whichever comes first.