My favorite story about that: I worked in furnace optimization, giant electric arc furnaces that use half the electrical capacity of a small town generation plant. These things use 'pencil leads' the width of a child, meters long, that strike an electric spark an inch or two in diameter and 12 inches long, from the probe to the pile of recycled steel in the crucible. Melt it for new steel.
Anyway we had a PC running an optimization on the arc length, probe distance etc to get the best instantaneous coupling, trying to save electricity by putting the energy into the steel (to melt it) instead of burning up the probe, creating heat etc.
One morning the plant called, had run overnight but sometime in the late night the thing stopped adjusting, ran 20 minutes before they noticed without moving the probe or adjusting the current. Just sat there burning up carbon and making heat.
You can see where this was going. Investigated, and the PC had gone into 'power save' mode, suspended the app, gone dark. Leaving the probe at whatever setting it was at.
I estimated at the time, that the power wasted during those 20 minutes was more than all the electricity ever saved worldwide by Windows 'power save' feature. Yes, it would have been better had Microsoft Never Invented Power Save, than to have had that incident.
You can say it was our fault, guy installing didn't remember to disable power save. But still, people do things like that. I prefer to blame the computer.