A theory I've heard is that any kind of diet is useful for losing weight, because it forces you to think more carefully about what you're eating.

But ditto, I've lost 50lbs twice in my life and both times were basically just via calorie counting.

Likewise, in my adventures in power lifting and body building, I gained ~25-40 lbs on several occasions. The only way to do this reliably for me was to count calories.

Once you establish your basic metabolic rate, it simply works. Yes, it is a pain in the ass. Yes, it's a lot of effort and discipline.. but the results are predictable and reliable.