As to the argument about idling diesels . In the old days it was always considered best to let diesels run. But, with modern diesels with there modern fuel injection systems it makes no difference. In fact it is best to shut them down.
So it depends on which diesel engine you have and how old it is.
Same way with cold starts. I have a 1983 farm tractor at my place for snow removal and to run the emergency generator if needed. ( I had to run the generator for 3 days straight a couple of year ago after a big ice storm) If it is below 40 degrees outside it will not start without hitting the ether button once. Below 30 you have to hit the button several times. Below 10 it is simply not going to start without the block heater being plugged in ahead of time.
Our new tractors will start up in any weather without any of the above. It's not good for them so we plug them in, but they will start. (They do have glow plugs but, the glow plug light only stays on for a few seconds if it comes on at all)
My brother starts his 2015 f-350 all winter long without plugging it in. And, he has never even seen the glow plug light come on. Heck, I don't even know if it has them. It just fires right up like a gas motor.