For LP operation only, you can leave those switches off. Or you can use those switches for electric only operation and save your LP. You can run LP and electric at the same time for faster recovery. DO NOT turn those switches on without water in the heater tank! The electric element will fry itself in seconds if it is not surrounded by water.
For electric use, I leave my breaker on all the time and use the switch on the water heater to turn on and off. I don't like to cycle my breaker if I don't have to. That's just me, others will disagree.