Whether or not to turn your computer and monitor off after daily use is a point of confusion for many. The bottom line is turn them off. And better yet, unplug them. If you work in an office environment that requires you to leave your PC running so IT can push out system updates, at least turn off your monitor. Here’s a good look from Microsoft at some of common myths regarding turning your computer off or leaving it on…

• Turning your PC off uses more energy than leaving it on.
  Not true. The small surge of power you use when turning it on — which varies per PC make and model — is still much smaller than the amount you use in keeping it on for lengthy periods.
• Turning your PC on and off wears it out.
  A decade ago, there was something to this, but not today, say Hershberg and others. It used to be that PC hard disks did not automatically park their heads when shut off, and that frequent on/off cycling could damage the hard disks. Today’s PCs are designed to handle 40,000 on/off cycles before a failure, and that’s a number you likely won’t reach during the computer’s five-to-seven-year life span.

• Screen savers save energy.
  Not true. Screen savers, at a minimum, can use 42 watts; those with 3D graphics can use as much as 114.5 watts, according to Don McCall, a Dell product marketing manager who does power measurement studies for the PC manufacturer. “It’s absolutely wrong thinking that a screen saver will save energy,” he says.
• Your computer uses zero energy when “off.”
  That’s true only if it is unplugged. Otherwise, the PC utilizes “flea power,” or about 2.3 watts, to maintain local-area network connectivity, among other things, McCall says. In “hibernate” mode, your PC uses the same 2.3 watts; in “sleep” mode, your PC uses about 3.1 watts. Monitors do use zero energy when turned off.

The Department of Energy also has a take on this that provides clear guidelines…