Hidden interface controls that affect usability

The rotational On-Off switch for a computer is cool and provides excellent feedback, but like many stateful electromechanical input elements it has the problem that it might run out of sync with the system it controls. E.g. what if the PC is shutdown, it is practically off (you can't do useful stuff with) but technically on (only in a weird shutdown state).

I am a fan of the conceptional clarity, but having to wait for my PC to shutdown only to have to flip a switch myself is not good UX. The absolute ideal would be the switch mechanically turning to off once it is off, and such switches exist, but they are expensive and require extra electronics to drive the electromagnetic part. A really good example of this UX principle are the motor faders in digital audio mixers: You can move them with your hand but if you cange to a different channel layout the mixer can move the faders for you. The downside of those is mainly cost.

The cheap 80/20 solution for the PC is a momentary push-button and a Green/Red LED to display the current state. 5s holding is power-off because everything else has the danger of accidentally switching off — but this isn't obvious to the non-initialized.