[marcus0x62]

You use the information to monitor and guide your training, for one thing. A lot has been made about how smart watches aren't particularly accurate when measuring things like sleep or HRV (as compared to laboratory equipment,) but there is a kind of stochastic reliability good personal monitors provide. When my garmin watch says I'm fatigued (because of low HRV) or haven't been sleeping well, I see a difference in my athletic performance and can adjust accordingly to avoid injury.

It may not be super accurate at monitoring HRV, and might not even really be monitoring HRV, but it is monitoring something that correlates highly to how I feel and am likely to perform.