It is a useful hormone because as leptin increases it is supposed to shut off appetite and motivate activity to burn calories.
It has been show that as obese people become fatter, their leptin levels rise (as expected), but there is a problem. You see they actually become resistant to the actions of this hormone thus causing hunger to remain elevated.
A recent study was conducted to investigate Leptin and exercise. This study involved obese post menopausal women. It was confirmed (as expected) that these post menopausal obese women had much higher leptin levels than in lean post menopausal women.
During intense exercise, these obese women did not have reduced production of leptin but the lean women did. However during moderate-intensity exercise the researchers observed lowered leptin in obese women.
Intense exercise does not lower leptin but moderate exercise does. This suggests that obese women who undergo intense exercise will not feel as hungry as when exercising moderately.
The researcher is quoted to say “Obesity interferes with leptin’s detection of exercise energy expenditure and with appetite suppression. Obese women perhaps need to consciously watch their calories because some of the hormonal satiety [fullness] signals don’t seem to work as well.”"
Here is the studyTweet