heart rate training
Even if your goal is to burn off fat, you don't want to solely work at low intensity for long periods of time without ever incorporating higher intensity bursts or intervals. This is true for not only the average person trying to get or stay fit, but also for the very elite athlete as well. No body is immune to consistent training in a zone that is too high or too low.
The next immediate question then becomes, how do I know what "zone" I am in? A Heart Rate Monitor gives you this exact information. Commonly, and mistakenly, people think they can judge themselves on how hard they are working. This simply is not true - for even the most body-conscious fitness professionals or lifelong athletes.
A difference of just three heart beats per minute can be significant enough to impede your progress. By exercising "blindly" on feel, people are missing out on utilizing one of the most important tools that can literally revolutionize their workouts and get results! The ONLY way to properly monitor yourself - whether performing a high intensity or lower intensity workout, regardless of your fitness goals - is through the use sports scientific testing and a heart rate monitor.