When Do Machines Sleep?

Our home is on a lovely lot at the back of a quiet cul-de-sac, but it's also at the back of the residential zone. Thus it is that when I look out the kitchen window, sometimes I can see a crane. This morning I saw it pull away, off to work. This evening it was parked again, and I thought "how nice... it's home from work and gets to sleep." (Yes, I had just gotten up from a nap. A cartoonist's life is rigorous and tiring.) And then I got to wondering idly about sleep, and whether any of our machines are complex enough to actually need it. Sure, they need maintenance. Some even need to be left "off" for periods of time -- especially machines that generate lots of waste heat. But what about SLEEP? Do we have machines that get annoyed with us if we ask them to work during their planned nap? Will any of them go quietly insane if we don't give them a little dream-time to themselves? Of course not. They are all far too simple, and besides, we are not about to build machines that suffer from something as inefficient as a requirement that they spend a third of their time sucking power while not getting any work done. (I am very carefully ignoring the fact that my computer is very sluggish when I try to use it on Saturday evenings during the scheduled virus scan. And don't get me started on the Sunday Night Backup.)