I use a powermeter for training and riding and I monitor my HR but don't really do anything with the HR data. I have enough power & HR data over the past 4 yrs that I could use HR to track training load as effectively as power if my powermeters went out of commission.
I look at power when taking a pull on group ride just to keep it steady and during intervals or TTs but mostly I just record it and look at the data after. When riding I probably ride more by RPE than holding to a specific power number. I'll look at my power which tells me how I'm doing on that particular day. During a race I don't look at anything on the computer unless I'm in a break but I do enjoy reviewing my data and that of others afterwards.