Although I usually write important stuff on pieces of paper or on a calendar, it is also good to use an agenda book because they keep you organized and up-to-date. It is also good to carry an agenda book to class or at a meeting to write down the due dates for your assignments in class and at work.
Regardless, academic and non-academic planners are as helpful and mostly organized like a regular calendar (Although they are not placed on the refrigerator).
When you have an upcoming meeting, use the agenda book. The point of using this planner is to keep your work in order.
What object, other than an agenda book, would you use to keep your work organized?