I guess I prefer to have it and not need it versus need it and not have it.
We don't run the Onan for air conditioning. Like some folks have said we try not to go places where we would need it. Only when we need to run the microwave or our coffee maker. Or anything else that needs more power than my 400W inverters can supply. Your inverter should handle those functions. Since adding additional battery and inverter capacity would be complex and pricey on our old rig, we use the Onan when we need 120V AC.