For example, oxygen saturation monitoring revealed my at-rest breathing reflex is completely broken due to a known genetic flaw. You know the memes about 'your breathing is now under conscious control'? Mine actually is.
That led to a sleep study-- and, yup, I don't breathe when I'm asleep. I wake every two or three minutes, all night, take a few breaths, and go back to sleep. And have all my life. The mystery of why I'm 'such a light sleeper' also revealed.
Doc I saw about it remarked the mutation is probably more widespread then we know because 'no one is looking for it'. It also completely freaked out a few anesthesiologists.
[There are other reflexes around breathing, and no, I can't just hold me breath as long as I want. The physiological reminders to breathe are pretty strong! But I routinely see my SP02 at rest drop below 70.]
The realtime feedback is useful and actionable. Breathing more slowly, exhaling more than inhaling (counterintuitive), pausing, and breathing through the nose definitely make a difference for me.
But everyone is a little different so you have to experiment. Breathing is very multidimensional and hard to explain. The Nestor book is a good intro, and I've mentioned it on HN a few times before.
I'm a big believer now. It is almost laughably simple, and I have to cite the fact the fact that no company profits if you breathe better, sleep better, etc. It's a trite saying but true ...