Andy/Ironhed,
I didn't log my first 5 years of diving, but I wished I had. When I became an instructor 29 years ago it became the thing to do, and I'm glad I finally got started.
At first it wasn't easy, keeping a paper log, but I liked to draw out dive sites and keep track of the divers I met, where we were and what happened. Since 1995 when I got my first downloading computer it became a joy!
Now I can show you thousands of dive profiles, seasonal reports on temperature, visibility, and marine life... along with what fish we speared! I teach all levels of dive classes with them.
I also keep a brief Captains log, and can compare it to the dive log. BTW, when I took my Captains course I didn't have to fudge my "on water record"... it was in my dive log.
Since I started shooting video and U/W photos about 18 years ago, and digital topside photos since 2000, the collection has augmented the history.
All of the recorded dives I've done over the decades have become my personal references, for articles I've written and even just for online posts. Having pertinent details to quote makes all the difference!
Chad