More like, "here's the times I went to sleep and woke up in the previous month. What can I expect today?" Hopefully including the effects of caffeine, delayed sleep, early awakening, etc. My sleep may sort of follow a cycle, but it's not regular enough that knowing the cycle would be that useful.

Here's the raw data for 6 months or so last year: Data.

EDIT: I was unemployed during this period, and not using an alarm regularly, so I was sleeping exactly when I felt like it. If I was working it would look much different.