Bypass valve

[dj-Harry]

Does anyone know exactly what the 1/4 turn valve on the white hose is for. I’ve been told it’s for winterization and bypasses the heater, even though there is a heater bypass valve (red handle). I’ve been told to keep it open and closed when using the system, by different people at the dealership. It appears that the water pump (off the fresh water tank) only works when it is in the open position. Should that also be the position when using the city water hookup? Is it only closed when draining the hot water tank for winterizing? There is no documentation on this, that I could find. See attached photo.