I've been journalling for 10+ years. In addition to forcing me to actually write down what happened that day, reviewing old entries provides a feeling of history that makes life feel soooo long and so rich. I can review my now-wife's rocky courtship and feel grateful we made it. I looked back 3 years ago and found the day our children were conceived :D (we have twins). I can review the anxieties of my PhD years, etc…
I don't disagree. But I think the flavor of the richness depends on the quality of the days. It is my experience that decades can also be built from days that ought not be preserved.
Or at least not without strong curation and editorial treatments.