If you leave your home for an extended period of time or if no one is living at the location, any appliance you leave plugged in or connected will continue to use electricity even while you are gone. Your water heater, freezer, refrigerator, HVAC system, landscape irrigation, well pump, pool pump, etc. keep on running when you're not home. Also, any appliance or electronics that have a standby feature or clock, constantly draw electricity.
Before you leave, make sure to turn off or unplug appliances that aren't needed and adjust your thermostat to help keep heating and cooling costs down.