I got an iWatch from my kids a year and a half ago. Elevation gain was my primary reason for wearing it, but I like the HR monitoring.
Over a period of time it becomes more of a post ride reference, except for those segments where I know I’ve really pushed myself; then I’ll glance at the reading. I don’t think there are wrong or right numbers, you just have to establish that range yourself.
A cardiologist and stress test can help to define where you want to be. Obviously if something pops up, you need to address that, but if you are clean and have good recovery, just ride how you normally do and note those times when you feel you really reached a limit.
John