I used to keep one religiously between the ages of 14-29, and now I have a journal that i write in everynow and again.
I found them all a while back and got rid of them, I was with a guy for 12 years from 16-29 and re reading them i wondered why I had not left him sooner!
I kept some, where me and my mum had done lots of things together at the time and she died a few years ago, so this is something really nice to look back on and remember specific times and everyday stuff you do with someone but dont always remember, if you can understand what i mean by this