Biometrics
This is a completely unnecessary part of the hobby - I actually strongly advise against it unless you're a total nerd with nothing better to do.
Caution
I want to begin by saying that if you find that you're stressed out by what you see when you track biometric data, or you let yourself become affected negatively by your results then I don't think its worth tracking them. I used to track my sleep in 2018 and it almost exclusively made me anxious and have a bad day since I almost never reached my sleep target and it would constantly make me feel like I was unhealthy (which was true, I was my fattest in 2018).
The watch I used to track my sleep in 2018
Some of my bloodwork results with dates