I usually see owners/drivers of vans (Hi-Ace, Urvan, Starex, and the like) running their engines with the aircon on for several minutes like for more than 30mins to an hour at the parking area. I know these are diesel engines. But is this okay? What are its adverse effects, if any? Fuel consumption? Is this practice ok because they are vans? what about SUVs doing this, what would be their difference?

How about those cars on gas engines also doing this practice of running their engines with the aircon on for several minutes?

Pls enlighten me on this. I am not doing this to my ride (Fortuner Diesel AT 2016), but still I am curious.