I agree that a dive log is first and foremost a journal for the diver himself, and a data base of information on equipment, weighting, gas consumption, and dive sites. However, it is necessary to demonstrate logged dives to PADI when entering into a level of professional certification. Unlike other posters, I and my wife have been asked for our logs to prove experience levels for certain dives. I am sure an electronic log will suffice for those kind of purposes given the e-mania of the past ten years. I however prefer the traditional log book, and like an earlier poster have several "volumes." I keep old pages in loose leaf binders, and maintain about the last 100 dives in my current log. E-logs have improved so that you can input more information than in the past, but I like to note things besides gear worn, weight used, water temp and gas consumption. I note what I saw, what I did, who I did it with, and things like that. I enjoy reading log entries when I am between dive trips or training weekends. I encourage you to log every dive, and use whatever format of log that will encourage you to do so. As for those who think logs are unnecessary or trivial, I am sad for them. They have lost the opportunity to create a personal database useful in dive planning as well as a creative record of good times.
DivemasterDennis