How does “optimize storage” work?

Hello,

I have a question regarding optimizing storage using iCloud for Photos. I have read that my iPhone keeps the photos I look at the most in high resolution (if storage capacity allows that) whereas other photos are only stored in low resolution on my iPhone.

Does the iPhone frequently analyze, which photos I look at the most? For example when I suddenly look at an old photo on my Wi-Fi, iPhone will download the high resolution variant, will it stay on my phone and some other not as much viewed photo will get transfered to iCloud?

Thank you for clarifying.