On a motorhome the AGS will start the generator when the house battery voltage is low. If you are plugged into shore power, and your inverter is on, and you have the AGS set to ON, a loss of shore power will eventually drain the house batteries and the generator will start to recharge them and provide AC power. It will shut off once the batteries reach a certain voltage, and let the inverter do its thing again.
It is a bit different from a home backup generator that will start, almost immediately, when grid power is lost. Most homes donít have a battery backup, or at least one that can be charged by a generator, so the generator will run until power is restored or it runs out of fuel.