Most people schedule routine maintenance in the wee hours. If you have
such, leave it on.
Turn all of it off when you're gone for an extended period.
Some run their TVs, stereos, PCs 24/7. Some run their AC in the spring and
heat in the fall instead of opening their windows too, even though its
comfortable outside, windows screens and security aside. Some leave their
vehicles running when parked at the convenience store. Some people race to
each traffic light, impeding traffic that's coordinated with the traffic
lights.
The required wattage of a PC has increased for the newer PCs. There's well
over 300 million people in this country, should they leave their PCs on or
off when not in use?