Rest mode uses residual engine heat to keep the car warm for up to 30 minutes after shutdown. i.e. you can shut it off, turn rest on, run into a store and come back and the car will still be warm.

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record