It&#x27;s evidence to show people (family, doctors, etc... and yourself). It&#x27;s harder evidence than flaky human memory or &quot;impressions&quot; of how I slept, in any event. You can literally see how crappy your sleep is, on a chart. It&#x27;s rather eye-opening, and if you have a wife or girlfriend who wonders why you&#x27;re a space cadet today who can&#x27;t get anything done, you can always point to the &quot;4 hours of good shuteye&quot; chart from last night (if it exists) lol