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

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!