Improve your productivity.
The aim of the planner is to help you see your short term goal, your long term goals and your deadlines. It's designed to help you prioritise.
Keep track of important tasks.
The planner helps you to remember the important things, i.e. reviewing policies, meeting with governors, or staff's birthday etc.
Be more organised.
Being organised can save a lot of time and energy which could be focused onto other areas. All your notes of meetings and appointments can be recorded in your planner.