I'm working on a sketch where an Arduino UNO performs no useful work after the first 10 minutes following power on. It is not needed again until power to it is shut down, then re-enabled. This may not happen for hours or even days. No wake-up function is required, or deemed useful.
Of course, the Arduino could simply be left on as long as it's connected to its power source, but it will be placed remotely, and it seems [to me] safer to have it powered off. when not in use.
In essence, the Arduino is powered by a wall wart and plugged in with other devices fed by a switchable 120v power source.
I found a couple of possible hardware/software solutions to the problem but it isn't clear whether they would work in this situation. Power consumption is not the issue here.