Heart Rate Training

Yes. Firstly- you asked about training, so how I use HR during training is different than on race day.  We'll talk about training.

If you live in a flat place with minimal wind, or run on a track, then using pace as a measure of intensity is pretty solid.  If when you race, you're also on flat areas, then you can use your race paces to calculate training paces- and you're good to go.  Me, there's little that's flat near me, so pace is a poor metric.  Then, you need to look at 'intensity'.  So, how do you judge your intensity.  you can do it by feel, i.e. RPE (rate of perceived exertion), HR, or for cycling- a power meter.

power meters for cycling are the bees knees, but the running ones are just getting there.  Not well integrated and developed yet.

Roughly, I find that RPE gets me within about 20% accurate (emotions play a huge role here), HR within about 10%, and a power meter 2%.

Key thing about HR is that while it's a really good metric of intensity, you need to be aware of the things that can affect it.  Fatigue, hydration and temperature are the primary factors.  So- whenever you look at your HR, you need to always be compensating for the 'extra' things that your heart is doing, while it's also sending blood to your muscles.  You'll only learn the effects by doing a lot of HR training.

Now- with all of that in mind.  Yes.  HR training is very valuable.  With running, most of your running should be easy.  i.e. zones 1-3.  You can look up how to set zones, there are minor variations between methods but all shoot for the same thing.  Ignore your Max HR.  That's almost irrelevant for endurance sports.  What you really need to measure is your Lactate Threshold HR. LTHR is the HR you can sustain, on race day, going all out, for an hour.  It defines your current physiological limit and is the number that is used to calculate your zones.

Bottom line:  For training, I mostly use my HR to keep me from running too fast on easy days.