The inverters are also sold for use as uninterruptible power so they are designed as pass through for utility power with the inverter in standby ready to switch in less than 2 milliseconds. generally, you don't need this in an RV. It draws about 2 amps from the battery on standby, so I suggest turning it off except when in active use. I keep mine off. It draws nearly 4 amps when on and active with no connected load. It draws 0.02 amps when off
Edit: the inverter provides 120V power for the entertainment system and (very) small appliances when you don't have shore power.