And drains the battery.
I don't think there is going to be a huge difference in the remaining power in your battery, as when you're in sleep/hibernate/standby whatever you call that, the only power that's being maintained is your RAM which consumes negligible wattage (didn't crosscheck and researched but this is how I understood it). Besides, the battery has also internal resistance which will make the battery drain even if it's unused or even if disconnected.