Another reason to have the battery switch on (in Vegas & Axis it is called the USE/STORE switch) is so that the engine driven alternator will charge the house batteries while yo are driving.
It's real important to remember -- the house batteries will not charge from shore power, generator power, or the engine-driven alternator unless that switch is ON.
Ed & Bev Felker
Retired USAF Col and retired Nurse
Traveling with Lily & Bella ('Teddy Bear' breed)
2015 Vegas 24.1 (E-350)