[TomT]

Running the engine just off the battery will shorten the battery life.

Draining down the battery and then periodically turning on the alternator to recharge it might shorten the life of the alternator. (A new ACDelco alternator for Unklecueball's '06 Aveo is $390 per RockAuto.com)

Modern cars like the Aveo already use the smallest, lightest, lowest output alternator possible.

Turning off major electrical accessories when stopped at a light would increase gas mileage because the engine would not have to automatically speed up to avoid stalling. But turning off headlights at night might be risky!