Leaving your printer on depends greatly on whether you have a laser or inkjet printers. Inkjet printers waste relatively low amounts of energy. When inkjet printers are not being used, they normally go into “sleep mode.” Laser printers on the other hand, use up a lot of energy whether it is on “sleep mode” or if it is actively printing something.

Leaving your inkjet printer on, takes very little power. While your inkjet printer is on, every so often the printer sends a signal to cycle the ink in the heads so that it doesn't clog. If you turn your printer off, the next time you turn it on, it will undergo a cleaning cycle which tends to waste a lot of ink. The excess ink is soaked up by the waste pad beneath the printer. When the waste pad is full, the printer stops working. Unless you want to spend more than the cost of the printer or waste a lot of time on a messy cleanup you will end up throwing the printer out. So shutting it off actually shortens its life.

Laser printers on the other hand work differently. They do not undergo a cleaning cycle like the inkjet, every time you turn it on. Laser printers are also large energy consumers. So I recommend that when your laser printer is not in use, turn it off.