I would have guessed the opposite.

Could you share a couple of these studies you are citing? Curious to read more.

Yeah, I only see anecdotal evidence of Apple Watch helping people: individual heavily-promoted stories.

Still, on a personal level, having my health data over time is something I find interesting to collect.

Things like my sleep, gym heartrate (I mostly pay attention to zones rather than specific numbers), sleep heartrate, occasional ECG reading, steps, with added smart scale and EMR data… It does show interesting trends over time.