I log all of my recreational dives. For me, it serves a couple of purposes. First, as was already stated, I can track my air consumption over time at depth. But, more importantly, my dive log is for me, not for you or anyone else. My dive log sparks memories. I always write down everything important from the dive. Depth and bottom time, basic grounds layout,current, landmarks, sealife, remarks on other divers, and so on. Anything good, bad, or otherwise. It's nice to be able to go back to the log before I return to a spot to jog my memory about the cool spots, nice view, etc. Also, as a new diver, I like to go back and look at my log, to find any mistakes I made, or maybe saw others making, and learn from those mistakes. IMHO, it has made me a better diver. As for it being a money grabbing device, mines a basic graphpaper notebook.
