I never idle below 1600
RPM for extended periods. It allows EGT to fall and wet stacking to occur, from what I'm told. I will however "idle" at 1600
RPM for up to half an hour depending on what I'm doing (chopping wood and hauling back to the house, etc...). If I'm getting off the tractor and putting myslef in a position where I could be injured, I shut it down regardless.
My neighbor is a long haul driver. He almost never shuts his rig down. I know, I can hear it at the bottom of my hill ALL NIGHT LONG! I've never asked why but I'm assuming it's the "cold" start. With 80000 lb. GVW you probably don't want to lug it around on a cold engine.