I think you can get a lot of useful information from journals or diaries and I believe they do serve a useful purpose. I have very heard recently that making them be in too much detail can take away from the fun of the activity by having to either make notes on the run so nothing is forgotten or racking your brain later so nothing is missed.

I believe there may be a happy medium ground and if you and your sub have found that compromise then it works for you and that is all that is really necessary to make you both happy. However if it becomes a chore, no longer enjoyable to either one or both of you, then something must change. Until that time, if ever, enjoy.