OK to leave it on when you are AT the campsite, since it only is on (pumping) when the system calls for pressure (ie. when you turn on a faucet).
However, we turn it off whenever we leave the travel trailer or immediate area and at night (only turn it on to flush on nighttime toilet trips). With it off, any leak will only spill a small amount until the pressure is gone. With it on, a leak will empty your entire FW tank into the travel trailer. Same for when hooked up to campground water - turn it off at the spigot when not at your trailer or else a leak could be disastrous.