Interesting question.
My personal preference would be to never operate on "both", because of inevitable uneven feed badly indicated by the semi-useless Cessna gauges, and because if you do have an empty tank on one side, then selecting "both" will draw air from that side, and probably not fuel from the other. Controlled switching between left and right is more likely to give me balanced tanks, in my experience.
After shut-down, I'd normally select "off" ! The worst that happens then is that the next person to try and fly can't start the engine until they've done their checks properly.
G