The Online Family answers:

There is a lot of debate over whether turning off your computer each night saves or wastes electricity. On one hand, your computer is off and not using power. On the other hand it takes more energy to power up the entire system than it would if you powered up from "sleep mode."  So to cut down on your electricity bills, consider putting all your computers in sleep or "hibernation" mode at night. Turn off your monitor and other peripheral devices like printers. And check out your Settings menu for "Energy Settings" which allows you to set a schedule to put your computer to sleep at night or when you're away from it for longer than five minutes, for example.