It's kind of open ended. Id like to track as many things as possible, so that I can see what instigates a flare, or what leads to my low energy days.
I also used a lot of the health functions on my iPhone, but those are easy to ignore.
I also used a bunch of smart buttons - so when I drank water I pressed a smart button to log that, I had other smart buttons to log taking specific medications, etc.
The problem is if you’re not motivated to do it (which is often the case if you’re feeling unwell/overwhelmed) then very few systems help.