Whoever told you it's bad for the engine is full of hogwash. I let all my cars, including my 300SDL idle for extended periods all the time. Alot of days my cars ran for 12-14 hours non stop. I do alot of stops and feel it's bad for the engine to stop it then start it several times a day. When I run into a dealership or grab a cup of coffee, I leave it running. When I plan to be longer than an hour, then I shut it off. Alot of times in cold weather, hot weather and snow I let my cars idle for extended periods (1-5 hours). Better to keep the engine hot and lubricated. Make as few cold-starts per day as possible.