As someone who has to make sure a fleet gets maintained, I can assure you excessive idle time is rough on them, Ford says every idle hour is equivalent to 30 miles, we have 65k mile cars in our fleet with 18-20k of idle time, I can assure you that they are smoking piles of $h!t.
A neighboring department had a fleet of ecoboost car that would eat turbos every 10-12 months, one again, hot seating the cars and excessive idle time. If leaving them idling was good, dealers would just leave them run on the lot?
Ford did void a warranty on one of our F550’s, the truck had 9k miles on it, but had 1k idle time on it, motor gave up, and even though Ford fleet said that they would never use idle hours to void a warranty....... they did. Your mileage may vary....