When I had Covid I got value from tracking this metric. If it went below 90 I would have called 911.

Day-to-day, no value at all (I have it on my Garmin). Only in combination with respiration rate + HRV + RHR does it become a useful signal, and frankly, if all four of those are out of whack then the odds you feel sick or run down and don't need metrics to tell you so are very high!

Due to spending more time in a chair than being active I have a bit more interactions with Gravity than most. :) This has led to fairly significant sleep apnea, which is most easily tracked via monitoring of O2 saturation.

The Apple watch data isn't really useful for this at all as the frequency of monitoring is just too low. There are a bunch of ~$100 devices that you can get from Amazon that do a fantastic job monitoring O2 Sat for a night and have nice integrations into Apple/Android.

I do wish the CPAP's offered this type of integration - that is, they had a Bluetooth receiver to which I could pair an O2 sensor, and have the data coupled with my breathing analysis. This would be nice to have in OSCAR (the open-source analysis package) or even in Apple Health.

Instead, the manufactures like ResMed treat this data as a walled garden and try their hardest to require everything to go through a Sleep Doctor who pays them a non-trivial data subscription.

I really like collecting as much data as possible with my watch. I have found Apples analysis in the health app to be pretty helpful over longer periods of time. o2 probably the weaker of signals and to be honest I just like having it when I am sick. I will convince myself sick in bed I have Covid and then check my o2 and feel better.

Is that so?

It amuses me that Apple will block that EU mandated store stuff if you move a EUnphone to the US after a few weeks (at least I understand that to be the case) but doesn't do the same for this feature.