I use it with folks when they have demonstrated high cortisol levels via the Adrenal Stress Index test (Diagnos-Techs).
A typical symptom of this is when someone can't fall asleep to begin with or wakes up middle of the night and simply cannot fall back asleep. However, I want to have the test to be sure that's what is going on.
Using it willy-nilly is hit or miss. I just had an athlete test with low cortisol levels at every time point. PS would not help him at all.