I don't need my Fenix to track my heartrate (from wrist) all day but only when I start an activity (whatever it is: running, swimming, ...). The main idea of course is to save battery.
Firstly, the battery saving by Turing of WHR during the day is minimal. Secondly, it's not possible to do it automatically. You have to manually turn off, then turn on for your activity.
Been discussed on many, many occasions throughout the forum in any number of threads for devices with WHR.
