I recently purchased a heart rate monitor to that I could keep my training heart rate in the low end (94 to 111) to increase fat loss. I read the exercise heart rate charts at the gym and did some internet research and learned that "for optimum fat loss...make sure that you exercise in such a way that as many of the calories that you burn come from stored fat as is possible." You do this by keeping your heart rate in the fat burning zone (55% to 65%) and exercise for 45 - 60 minutes for 4 to 5 times a week. However, you also have to carefully monitor your calorie and fat intake. You have to burn more calories than you take in and eat a relatively low fat diet. Walking is an excellent form of exercise to use for maximum fat burning. Higher intensity exercise burns more calories in a shorter time period, but this type of exercise strengthens your heart. The source I read stated that "another nice thing about exercising at a rate that will give you maximum fat loss is that once you lose the fat you'll be in much better shape to use your aerobic exercise for strengthening your heart even more."
I have a LOT of stored fat. For me, exercising in the lower heart rate zone is more comfortable and I'm more apt to keep going to the gym and exercising if it isn't so taxing on my body. I know that when the fat comes off, and I feel lighter, that I'll be ready to increase the intensity. Fat loss does NOT equal weight loss. We're talking body composition here. All in all, I guess it's not as important as to how intense you work out, but that you do work out, and you do it consistently.
Just my point of view!