Also you can use them for things like Weddings, Holidays, Projects, Boatbuilding, Fishing, meeting management and sales targets, any thing that needs organising. The date book can be used as a personal journal, writing about day to day events. Especially on holidays and trips, which means that later you can return to it and find the name of that little fishing village, you had lunch in. Even the name of the restaurant you dined in. Or the names of the guys at that sales conference.
Notes is surprisingly useful.
This relative kept all his chemical data, colour mixes, types of polymers, fixers, and extenders. He was also working on a personal project hoping to make some chemical improvements to some inks for his firm. One day his firm asked him to train a new guy. After a few days the new guy was brilliant, and looked as if he would make top upper management with no effort at all. My relative was pleased for him, but dismayed at his own progress, it had taken him months to settle in and years to become proficient, at his job.