You're assuming most programs run start to finish then the machine shuts down. That's probably <1% of all machines. Most machines run on a loop. So when they do

You're assuming most programs run start to finish then the machine shuts down. That's probably <1% of all machines. Most machines run on a loop. So when they don't do stdio either they do some other useful computation (e.g. if a game engine is not stalled on stdio, it can process a few more frames per second) or they run an idle process which consumes less energy but very far away from 0. So, no even that logic doesn't work here. Saving 20% stdio cycles will probably not even have measurable effect on global enegy consumption.