Humans accumulate an ever growing collection of personal photos and videos as they get older. Eventually it will become like gmail, where you never delete them.
Varies from person to person. After my cat died last year I started remembering each and every photo I had taken in different places over the years and somehow I lost track of a single photo (I'm not sure how it never got put in a single cloud photo service but I suspect it's because I took it on a camera, not a smartphone) that stood out to me because I remember it as probably the happiest he ever looked. I felt pretty terrible given of all the digital hoarding I do I couldn't keep track of one stinking picture that would mean more to me than hundreds of 4K movies. I'm a bit more liberal with my picture taking now knowing what I went through after the death of a cat and with people it would be worse.
I once thought experience was enough for me, however I've learned that memory fades. I can only recall bits and pieces of things I thought I'd never forget.
There's nothing that jostles my memory quite as well as a picture.
The Google robotic overlord does a very good job at showing you interesting photos from years ago. I started taking pictures and forgetting about them only to be pleasantly surprised a few years from now.