I had a heart problem 8 years ago and used the HRM to give me confidence on what I was doing physically. No overstraining or higher HR for too long. So that is one reason- a check on a problem

However- I go out on some long rides. I have to pace myself on those rides so if I stayed in my upper reaches for too long- I probably would not make the distance. I know what my max is, and what I can get up to. I treat my max as 165 but I like to ride at about 140 BPM. at this rate I am fast enough, comfortable and I can do the distance. I will go to 150 for hills- get up to 155 by the end of the hill and even reach my 165 by the end of the trickier hills.

Only problem is that although I am comfortable at 140, I am also comfortable at 130. I am also once warmed up comfortable at 145. By using the HRM I can Keep myself in the zone of 140- so extending my ride. So second reason is to regulate my pace in the rides.

I have to do a warm up on all rides. I cannot get on the bike and go out and get to 140 immediately. I get myself to 120 and slowdown, When breathing comfortable- I then go to 130, then slow down and recover. Then go to 140 and recover and finally to 150 and slow down again. Once I have hit that 150 and recovered- I know that my warm up has been successful and I will be able to do my ride without letting myself down on the ride
Then somedays I will not warm up right and find myself Working hard- but a quick check on the HRM will show me that I am at 130. If I have not done the warm up right this will occur- so slow down and do the warm up again. If I still feel uncomfortable at 130- Then I know it will not be a good ride or I am about to come down with a cold.

I am not a slave to the HRM and I don't wear it that often but If I am in training for an event or actually on an event, then the HRM will be used to keep an eye on what I am doing.

Plus the fact that as my riding partners know about the Heart problem- It scares the Sh*t out of them when we get to the top of a hard climb and the alarm goes off.