Unfortunately, turning on and off your computer is bad for the components inside. While a computer is on, the chips can reach temperatures of well over a hundred degrees (that's why there's a cooling fan inside). Turning off the computer makes the chips cool, and subsequently, contract. Repeated expanding / contracting may lead to processor problems and will definitely shorten the lifespan of your components. The monitor, however, should be turned off -- it uses as much energy as a television and puts out twice the electromaginetic power. The computer is a low voltage device and the few dollars you dave in energy bills will be lost in replacing your computer components after failure.