well
At 60-70% HRM the highest percentage of calories burned, after available fuel, will be from fat.
At 70-85% HRM you will burn more calories than at 60-70% but the calories burned will be taken more from protein stores than fat stores.
You always have to remember the body will use food/fuel that is available before returning body stores to food. I try to run at 60-70% of HRM because I find that I can go longer and consistently return to the exercise time and again. When I exercise at 70-85% HRM I feel used up after the exercise and sore the next day or days. I do exercise at 70-85% at times, but this is more for strength/muscle building. I also do not do the anaerobic exercise as often as the aerobic exercise.
Another point.
While aerobic exercise will help your body grow the muscles needed to accomplish the task at hand, it is a slow build. Anaerobic exercise breaks down muscle forcing it to rebuild stronger than before. More muscle = more calories burned at rest. So both forms of exercise are needed.