Did you also say he dumps the air?I remember I set the trailer brakes at a customer because he had a steep dock minutes later they were froze lucky for me the guy that unloaded me had a torch.That must happen a lot there.
I always set them when I was otr. Even in the winter. Mainly cause I had a horrible teacher and didn't know any better. However, my brakes never froze on me. I guess I got lucky. It was -50 windchill in Indianapolis 3 years ago. 20 inches of snow. I think I was one of the few where my trailer brakes didn't freeze.
Plus, if you are a team operation, you'll be having a crapping, no mile week anyway if you have to stop long enough for the brake to freeze enough to actually freeze shut. That and hes right. 99% of the rare time it does freeze, it's simply tap the brake drum with a 3lb sledge hammer and they pop right open. In that case, why not opt for the extra breaking. The fun one is our yard. Day cab work, so running 100-300 miles round trip with the trailer then dropping it for the next person to use. Always freezing up, but the fun part is I haul a drop deck van most of the time. Breaking loose the 17.5" tires is a lot worse than the 22.5's
I ran a lo-profile, trombone, step deck for quite a while... I know the pain. I had the perfect combo tool for that though. It was a ~2 foot long, 1 inch diameter, six-sided, solid bar. It worked great for slipping through wheel holes and then hitting the end with a hammer to loosen brakes (no crawling under trailers), and also for using on the drop-deck winches when the load was wider than the trailer (which was... always).
And always a slight downgrade slope for a easy out. Sometimes you get up several times during a winter storm to pack it down some more. I like to see the ELS eat that....
If your trailer has a small air leak, sometimes it's better to set it before you go to sleep so you don't get woke up thinking someone hit you when the valve pops and bags deflate.
He'll set wet and warm trailer brakes once in sub-32°F weather. I've had to break free six drums on a triaxle stepdeck in -25°C weather with the trailer buried in a snow bank. First, you have to dig out the axles enough for you to crawl under the deck. Then, go about trying to find out which wheels are stuck (before knowing it's all six) without being able to drag it out of the spot to see them roll or not. It took an hour and a half. When I train new guys, they get the "don't ever set your trailer brakes in cold weather until they've cooled/dried" speech. Their question is usually "Why?". My answer: "Because I'll track you down and smack you upside the head for being stupid. No, but really, don't do it, you'll severely inconvenience the next driver who has to pull that trailer. Don't worry, you'll learn soon enough." And anyone who thinks a few taps of the hammer will break free a drum needs to come to Winnipeg in February. Get a driver coming back from a trip through Ontario with nice mild (5°F) weather, that nice salt solution on the road, soaking wet drums, then park the trailer before letting them cool/dry and it dropping to -22°F overnight. That takes a 5 foot pry bar and 10 pound sledge to break free.
I hear you about the winter thing but we're September so the question isnt about winter. I understand his thinking. You're going to get into the habit of only setting the truck, then one day you're going to be on a little grade, heavy with a couple of broken spring brakes on your truck.......