The HR monitor is like the tachometer in a car. Can you drive a car without a tachometer? Sure, but a sports car with a manual gear box is better with a tachometer.
Maybe I’m old school, but I had an HR monitor before I ever had a power meter. I keep an eye on it like I keep an eye on the tach in my car.
I also did dfa alpha 1 testing for LT1 and I found it pretty reliable at 120-130bpm so if I’m trying to keep things under LT1 I keep an eye on HR. If I do endurance+ (edge of zone 3) intervals during an endurance ride, I try and maintain 130bpm.