RV water pumps are 'on demand' pumps.........with switch in ON position pump will only run when there is a demand (open faucet/shower/toilet or leak).
Something that causes line pressure in either cold or hot plumbing to decrease.
Pressure switch in pump head closes-pump runs And when opens----pump stops.
Use it like you want:
Switch ON all the time (caution: turn off when away from rig in case of a leak)
Switch ON/OFF as needed
Can even have pump switch ON when connected to city water..pump is not going to run unless pressure drops and doesn't consume any DC power when not running (very minor draw for LED ON).
Having it on with city water connected will not harm anything