From reading diet boards, a lot of people find that their weight loss efforts are more successful with a compositional approach than just Eating Less. "Eat less" might be a simple rule, but implementing it is not so simple. Compsitional diets remove that problem, and appear to work for a lot of people.

I know there are a lot of HN readers who have used the Keto diet with considerable success, for example. And there are a good number of other diets that work for many people too whilst allowing an ad libitum approach to eating.