> Most applications spend 90% of their runtime waiting for IO anyway, so optimizations of this scale don't do anything.

Again, depends on what you are doing. If you are doing web servers, electron apps or microcontrollers, sure. If you are doing batch computation, games, simulation, anything number crunchy, etc: no. As soon as you are CPU or memory bandwidth bound, optimisation does matter. And if you care about battery usage you also want to go to sleep as soon as possible (so any phone apps for example).