The absolute values for heart rate vary from person to person and change as you age. But I do notice that my resting heart rate slowy drops a bit as I get fitter (e.g. during a marathon build) and will rise more suddenly if I am getting sick or not getting enough rest.
I don't really pay much attention to the heart rate zones on my watch, but I do have a pretty good idea e.g. where my 5k race vs marathon race vs really easy run heart rate lies. This can be one piece of information along with perceived effort and pace to decide if I should be able to push a bit harder on a hard run or take it a bit easier on on what is supposed to be an easy run.
People pay real money for smartphones.