AC: leave it on -- or turn it on and off?

Here's a question we hear a lot, especially during heat waves:

Is it better to leave air conditioning running at the same temperature all day -- or turn it off (or raise the temperature) when leaving your home?

The American Council for an Energy-Efficient Economy (ACEEE) says to turn if off or raise the temperature when you leave.

Turning it off and on saves a fair amount of energy and helps air conditioners work more efficiently, according to ACEEE. While it may seem that air conditioners work harder to cool a space down from 80 to 76 degrees, the units run more efficiently and dehumidify better. If you have central air--or a window unit with a thermostat--you can save energy by setting the thermostat to a higher temperature when you are out. ACEEE estimates that air conditioners use 3 to 5 percent less energy for every degree you raise the thermostat. ACEEE recommends a thermostat setting of 78 degrees or higher when you’re out.

Fans can help, too. Fans don’t cool a room, but the moving air makes you feel more comfortable at a higher temperature, allowing you to set the thermostat higher and help you feel cool while using less energy. Because fans don’t reduce room temperature, remember to turn them off when no one is in the room.