> computers truly are so fast that it wouldn't look any different to the end-user; a 1ms and 1us delay upon each keystroke is, to the user, practically indistinguishable.

Unless, of course, the 1 ms operation drains the users battery 1000x faster than the 1 us operation.

Efficiency is no longer about speed, it's about noise, temperature, and battery life. Speed is a happy side effect.