Originally Posted by SSP

It doesn't matter if you're burning fats or glycogen, or both, when you exercise. For weight loss, it's the overall calorie deficit (calories in vs. calories out) that matters.

If you go for a hard bike ride or run, you'll mostly burn glycogen. But, after the exercise your body will replenish your glycogen stores by converting fat.

This is why it's generally better to exercise at higher intensities - you burn more calories per hour when you exercise vigorously so it's more time efficient.