An indicator I picked up from the thread https://www.trainerroad.com/forum/t/inigo-san-millan-training-model/43552/1441 is about using RHR as a rough assessment of training readiness.
In one of the interviews, ISM mentions an example of an athlete whose RHR was 10 point higher than their average. In that example, he expects the athlete will do poorly on that day’s workout. There could be many reasons for why the RHR was off, but the data point alone was enough to lead to a change in plan for that day.
That stuck with me and I’ve used it since. By itself, it doesn’t cause me to change my plans. But, if I’m feeling off, it’s one of the data points I’ll use to assess whether I’m ready to do my planned workout.