If you do structured exercise - meaning regular exercise either in a Gym, or on a machine - or outside, walking, running or swimming etc as part of a programme in which you have goals to reduce weight, improve heart function etc - then quite frankly, you need a heart rate monitor and you need to understand the principles behind it, why you are using it and how to use it.

I don't think that it is possible to undertake a structured exercise programme without an HRM.

The best way to understand how to use an HRM is to read a book about it. When I started using one, I had a look at quite a few books and the best one that I found for understanding how to put a heart rate monitor to best use was a book by Joe Friel - Total Heart Rate Training which I have linked to Amazon.

It's a small book and only a couple of chapters really deal with how a heart rate monitor works - so there is not a lot of reading to do if you don't want to.

There is a Kindle version - but for me, a paper version is better when I want a reference book - as opposed to a story book, where I merely want to go from beginning to the end and then finish the book.