I love my Charge HR for this sort of stuff. It gives me data to double-check my sense of "Something seems off, am I always this stressed?" Days where I'm antsy all day tend to be days I have a higher resting heart rate. Days when I have a higher resting heart rate tend to come after a couple nights of less-than-stellar sleep. It's easy to guess that being antsy all day is nervous energy from work, but if it only happens after 4 days of 6.5 hours of sleep... the fix isn't to work on my resting heart rate via meditation, it's to get more sleep.
The great thing for me is that I have concrete actions that help fix specific biometric anomalies: going to bed earlier, drinking less/more alcohol/coffee, exercising more/less. I know I should do all of these things all the time, but being able to see the effectiveness of specific actions is really satisfying.