When I was starting to put together a photo studio I had no flash meter, so I kept logs for what I shot at, how the lights were set up, etc. Over time I acquired a flash meter and learned lighting ratios and patterns. The log book was never opened nor looked at. After digital came along, along with a Maxxum 9 and F6 and F100 which record that stuff for you, I never logged a single thing.
I need a log for my darkroom work though... it's like inventing the wheel again every time I go to print, especially color.