Powering computers when they re doing no actual work is wasteful. A television set playing out of sight could just as well be a radio. No matter how long one stands in front of an open refrigerator, the contents are still the same. A lamp on an end table provides better reading light than a four-bulb ceiling fixture. The doors and heating vents to guest rooms and storerooms can be closed.
Technology makes it easier.
There are thermostats that automatically allow home temperature to drop when everyone is at school or work and turn the heat back up shortly before everyone is due home. There are timers that turn lights off and on, cue coffeemakers, start dinner. There are energy-efficient light fixtures and bulbs. Newer heating and air-conditioning units use far less energy. Insulation always helps, and it pays its own way very quickly.