Wow, so many posts and all misinformation. It is AUTOMATICALLY OFF. You turn it ON with the button. If you are in traffic or it is hot, it will automatically restart the engine if the interior has gotten too warm. Naturally, the A/C is not running with the engine off.
I don't believe this is an effort to improve gas mileage. This is a "green" feature. People have turned off their cars manually at traffic lights for YEARS. This simply automates the process. I don't turn mine ON much, but it does seem to work very efficiently.
E92 M3 MR on Red/Black ZCP Sound
2007 997S - sold
2003 E46 M3 Steel Grey on Red- sold
1997 E36 M3 Arctic Silver on Black- sold