don't get too carried away with the HR thing. Always measure against yourself. Physiologically we're all different and some people just have a naturally lower HR. Having the monitor is always a valuable tool. For one, the zones, as you pointed out. But also for knowing when you go into the red. When I was cycling I knew what my max HR was (~180bpm), and I measured my effort based on that. If I was under, I had the capacity to push myself harder. If I was too high, I had to ease up.My sister-in-law was talking about following a mutual friend's runs on Strava, and being astounded by how low the guy's heart rate is for how fast he's going. Seems like Zone 2 training really works if you keep at it. Hard to lose the "no pain no gain" attitude though
And the fitter you get the lower the HR will get, but not by much. When I used to do intense training camps, efforts that would push me to 180bpm on days 1 and 2, would only have me at around 165bpm on day 3 onwards. But, once I let up from the intense effort, it would go back up again fairly quickly.