The one for the "house" battery turns off most but not all of the 12 volt items in the coach. That switch is mainly used when you are storing your coach for a long period of time. That will eliminate a lot of battery drain. As my coach is plugged in all the time I have never used the switch. I believe that by turning the switch off when plugged in it also stops the battery from being charged (I could be wrong on that).
If you have a switch for the engine battery it does the same thing, I have never had a coach with a engine battery switch so really do not know. To me it seems kind of useless as you do not have a battery disconnect switch on you car.
For most part if not storing for along period of time leave them on.