Dennis, explain to me why a dive professional "needs" to log dives. Your reply is very narrow, and not at all representative of why I don't log dives.
Why a professional should log dives (IMO): I'm not a dive professional, but I am an engineer and keep a daily log for reasons that relate closely to a dive professionals again IMO.
1. Record keeping for potential litigation. Keeping clear concise records of students, dive times, conditions, would probably look a lot better to a jury than not doing so.
2. Record keeping for potential QA Violation Query. Again, when defending you name, records will hopefully help this. e.g. When Joe Diver answers the PADI questionnaire that the instruction didn't have a rope for use during the CESA drill, but you can produce a log that shows you had a rope attached to a float on site for the last 5 years, why would you not have done it that day.
3. A simple and redundant way to keep track of skills for continuing educations dive requirements. I'm not talking about OW Training. I'd assume those are done with such regularity that the skills on any given dive day are memorized, much the way people in the sciences just know Pi. But if you are doing a Deep Diver Specialty and want to keep track of skills on the dives it is a convenient way to do so and document it.
4. Best practices for young DMs and new instructors. If you are mentoring a DMC your dive log could be a great resource for them to glean best practices from. It could be a great resource for new instructors to learn rescue diver scenarios from. Fun things to do on Discover Scubas, etc...
Of course if all you do is log site, depth, weights, and air, there isn't much use in the log to the professional.