Electrical appliances when switched off still waste energy if they're plugged into the electrical circuit (to the plug in your wall).
Though the energy consumption of each individual device is small, the sum of all the devices becomes significant. This electrical power is known as vampire power because the appliance "sucks" the electricity out of the power grid when you're not using it. It is also known as phantom load, and can reach up to around 10 to 20 percent of the total consumption in a home.
Not only is it a waste of energy, which is bad for the environment, vampire power takes a big bite from the monthly electric bill. Mwahahahahaa