You may need more carbs for ANAEROBIC activities, such as weightlifting, because your body uses it to lift the weight. Anaerobic activities don't work great on fat. Instead, they work to raise your metabolic rate AFTERWARD, which is how they help with fat-burning.

You may be able to GET AWAY with eating more carbs for aerobic activity, because you will be burning them off while running. But remember - carbs get burned off before body fat. So the more carb you eat before cardio, the less body fat you will burn while you do it.

Edited to add: when I took the clinics, they told me I should be able to talk the whole time I was running. Helpful if you have a friend to chat with.