One of my motivations is for my kids to be able to look back on their memories. There are a lot of things that they don't remember doing and I love the surprise when they see the photos.
The other motivation is that I have a bunch of old photos from my grandparents - some in scrapbooks, some not - that if anything may have a small blurb about who is in the photo and why the photo was taken. I don't want to pass down photos without passing on the names & stories behind them!
Lastly, I want my grandkids to see what their parents were like as kids!
