Not sure, but maybe at a preventative level? E.g. if your heart rate behaves a certain way after exercise or during sleep, maybe it indicates a stronger likelihood of having a blood clot.

Well I don't know, I'm not a doctor- that's why I'm asking the question, hoping that someone knowledgeable will answer with a concrete reasoning.

Your comment in its present form is quite pointless.

I had a couple of ECGs recently. I'm not sure if they could get anything approaching the same graph through a watch some distance from the heart (the ECG has 8 or so contact points around the chest) but I did notice that a good portion of the cardiologists judgement came from inspecting the graph rather than anything more complex.