I BET you didn't know about this feature [BMW E90 and others] HD

Sorry for the shaky video but I was holding my phone is a very unconfortable position and I forgot to activate the IS. The REST button will blow warm air into the cabin after the car has risen to normal operating temps and it can ONLY be initiated when the ignition is OFF. You can use it to keep the car warm when you are for a quick shop or stopped in traffic etc...you can turn the engine off and keep the interior of the car warm for up to 15 minutes OR until you turn the ignition back on.