Since it's quiet:

When I was a kid a guy at the parts store demonstrated to my Dad that when electrical power was needed, a generator put a load on the engine. After that, my Dad was careful not to run lights, radio, heater fan, or other non-essentials when he was trying to get good gas mileage.

I have continued that tradition, however, I have seen it stated that electrical draw on an alternator doesn't increase the mechanical load.

When low on fuel will it help to turn off electrical components not needed for flight?

Is it true of an alternator; an electrical power demand doesn't cause an increased mechanical load?

Or, does keeping headlights on during the day decrease gas mileage?

Thanks!

Ben