Run operating warm engine in standby

Hello, I have a question of a purely theoretical nature: Now in winter you see people at the motorway parking lots again and again, e.g. without heating, who sleep in the car after hours of driving. They let the engine run because of the heating. I don’t have it before, but I always ask myself: Does this do nothing to the engine? Possibly petrol in the oil or other problems? As I said, only asked for so much interest.