Sleep mode is useful when you take a short break to refill snacks, take a work call, or get the kids to bed before resuming. But it could theoretically be an all night function as well. People prefer to use this mode because of the faster boot times when you want to play again. It for the same reason you likely just close the lid on your laptop and not shut it down entirely at the end of every workday. Microsoft own support page doesnt give any indication that you should only use sleep mode on...
