[quote]
I’m not trying to be a dick here, but can someone please explain how any of that would be beneficial to a dog’s health, life, or existence.[/quote]
That’s easily answered. Dogs did just fine for thousands of years because they WORKED to earn their keep. Whether they were wild or domestic, they hunted, herded, pulled, flushed and guarded.
We train our dogs to do stuff because our dogs love being something other than a farting lump of fur sleeping in a kennel and eating chow from a can in a bowl for free just so they can shit on your lawn.
Even if people just hid their food around the yard instead of dumping it in a bowl their dogs would be happier. But dogs who get to do cool shit like pulling cars or sleds, or tracking people through fields, or running around an obstacle course have happier, healthier lives than those who don’t.
When you love your dog, you get a kick out of seeing them work, too.
People make dogs do stuff for different reasons, as has been noted. Some out of care, some people actually use dogs as working animals (I know a guy who hires himself out as a ranch hand in Montana who has 3 working collies), some do it for sadistic reasons, and there are a few that blur the lines.
I will say, though, that working dogs, in my experience, seem happiest when they’re working – work and play are hard to distinguish with them. They are definitely not happy being sedentary.
Now, if we’re to try to steer this back to OP’s intended question: are individual animals predisposed to being “fat boys” like their human counterparts? Ah, um… I guess? I’ve seen plenty of fat dogs, but as to how much is nature, how much nurture, and is the incidence of each comparable to what you might find in the human population, I don’t know. I’ve read (on some cheesy poster somewhere, but I think it’s true) that if your dog’s overweight, you need to go on a walk.