In colder weather, we do this to keep the heat on. Aside from that, I've always been under the impression that starting and stopping the engine, unless its spec

In colder weather, we do this to keep the heat on. Aside from that, I've always been under the impression that starting and stopping the engine, unless its specifically designed to do that like in the case of cars that stop the engine at red lights - adds additional unneeded wear and tear to the engine. turning off an engine for 3 or 5 minutes, assuming it was warm, won't make the engine loose to much heat. Turning it off for a half hour, in the case of waiting for someone to get out of an appointment or store - would make the car loose enough heat that the heater will need time to warm up again upon starting again. Not a huge deal; just an inconvenience. I've also been told in bad snow storms, don't turn off the engine if your just waiting, for fear snow or ice might cause it not to restart but I don't think this is an issue on any modern cars (> 2000)