I used it for a few years to help lose weight. When I first started logging food, I was amazed at how many calories there were in food, and became aware of portion sizes. I then tried logging exercise. I was amazed at how much effort was required to burn off a Mars bar or similar. I'd been overestimating my calories burned through exercise and underestimating calories through food. It really is easier just to eat less.
Supposedly for a man of my height, weight and age, I'd need 2000 Calories a day. But if I ate that much, I'd put on weight. I worked out my magic figure was 1700 Calories. More than that and I'd put on weight, less than that and I'd lose weight.