Often you are camping without connection to an unlimited water supply. That translates into short showers. Being able to shutoff or restrict the water flow can dramatically reduce the amount of water used while keeping the shower comfortable. The original shower head installed in the trailer had no way to quickly stop the water.
Changing the head to one with a flow control is a very easy mod. Our replacement attached at the top of the hose. Simply unscrew the shower head from the hose and screw the new head onto the hose. Some may come with a new hose. In that case, unscrew from where it connects to the wall.
One note, the switch will not completely shutoff the water. If it did pressure would build up, so it drips slightly. The water savings will still be substantial. So get wet, soap up, and rinse off with the flick of a switch.