Historically (like the 1960s) it was conventional wisdom that for big-rig diesel trucks it was more cost effective to idle for an hour or so than to shut down and restart. Much like with conventional fluoescent light tubes, much of the wear occurs during start-up and warm-up. Burning a couple quarts of cheap fuel to avoid that wear and tear was sound business.
Nowadays that’s a lot less true, but the way most folks learn to do most grown-up stuff is by osmosis and handed down conventional “wisdom” which usually isn’t very wise. Or at least isn’t very wise any more.
I generally think that the only people who are truly concerned about it are the people who are always talking about the sizes of other people’s junk.
it’s not only that, most of them had no cold-start aids like glow plugs or intake grid heaters. If the engine got cold, you stood a good chance of not being able to restart it before running the batteries flat. and God help you if your truck had an air starter. Most/all modern diesels have at least glow plugs, and with the multi-shot 30,000 psi fuel injection they start easily. I drove a 2011 F-350 with the 6.7 Powerstroke diesel over a winter weekend a few years ago, and one morning it was like -8F. Got in, turned the key, and after three seconds of glow plug pre-heat the engine fired right up.
here’s what cold starting a diesel used to be like (this one even has glow plugs):
This is what it's like now
Yep, they’re diesels… The big dummy. He’ll start them up and immediately get out to go do something incredibly important like suck down several cigarettes or sit on the porch staring out in space. :smack:
That is why I drive a small car and own a small gun. I’m compensating for my enormous penis.
I’m with scumpup that was a dumb post.
Where I work, all of us do it. They are diesel’s, it’s hot or cold outside and plus we really don’t care enough to shut them off…ever. I let my car idle too because I listen to the stereo and don’t want to drain the battery. My bad habit is that I exit a vehicle and leave the door open.
Oh I dunno. I was talking to a guy at work about whether to buy a new car, and I gave him one of my rationales, “As an American male, I only have 3 choices for hobbies: cars, guns and watching sports. I’m tending toward cars.” As a bonus, I would expect my penis to grow enormously. 
Well, they probably just leave the engine on because it’s eerie sitting in silence if you are used to the low rumble and vibration. But I remember that it used to be that your air brakes failed if you weren’t careful about the door on a school bus with the engine off, and they might have had that drummed into them at a young age.