There are many misconceptions regarding HRMs and their use:What good is knowing your maximum heart rate?
I already know how to take my pulse without a HRM....
I don't need to know how hard I excercise...
What good is having all of that information?
These are all good questions but they are not an ends.
What good is HRM data?If you excercise routinely, you have one or some of these goals in mind: improving physical conditioning, maintaining physical conditioning, or recovering from some injury. Lets look at how improving conditioning are benefitted with a HRM.
1) When used properly an HRM can improve your lactate threshold AKA your aerobic threshold (AT).
2) Because different exercises tax the body in different ways, a HRM can fine tune your routine to a specific exercise.
3) Improving your fitness is EXTREMELY dependent on resting! Not sitting-on-your-butt kind of rest, but excercising below a specific intensity kind of rest; a HRM finds that intensity and helps you maintain it. An HRM also helps determine when your body needs to rest
4) Hiking at altitude is a very different exercise than hiking at sea level. An HRM lets you calibrate your load effectively with altitude so that you can maximize your endurance.
5) Funny things happen when your conditioning improves. For example your resting heart rate decreases, you can move faster at a specific heart rate, and it becomes increasing difficult to reach your maximum heart rate.
If you'd like this article fleshed out some more, please post comments below and I'll try to find the time to fill in a few details.