He's 1) WASTING GAS 2) Putting MORE WEAR on the engine and REDUCING the effective engine life. 3) Not a good idea to ever leave your car IN GEAR then walk away.

It's the same as sitting in traffic in gear with the foot brake. It jsut puts extra wear on the transmisison...mainly the torque converter.

Yes, this will warm up the engine quicker. But the improtant question is WHY??? you don't need to "warm-up" the engine before you drive off. Give it 5 seconds to reach a steady idle and drive of slowly. Jsut don't go full throttle or redline the engine until the temp at registers on first 2 marks of the gauge.

This is a production vehicle designed for the street. Not a F1 car that revs to 18,000 RPM about to be driven wide open on a racetrack. You don;t need ot warm-up the engine.