It's not that cut and dry.
I have sleep apnea and use a CPAP machine (hate that stupid thing). I'll wake up in the morning and think I slept ok, but a few hours later I'll think, "I must not have slept very well last night." Other times I'll wake up feeling dog ass tired thinking I slept crappy and once I get to work I feel ok.
All waking up tired measures is you woke up tired. There's no data behind that. Maybe you did sleep ok, but got up 5 times to go pee you don't remember. I work doing data analysis, so I prefer hard numbers to analyze rather than probably incorrect assumptions.
In my case, what does it matter? If I can bring in good data to my doctor, that's of value. I don't have to hand in the SD card from my CPAP anymore and I'm not sure how much data that thing really captures anyway.