I have been using a calendar for many years now and I have seen many people using it as weel for their daily schedule. Although I never asked myself whether I was using it the best way possible.
It is easy, you write down your meetings and duties so to keep track of everything you must do and don’t forget anything. Besides that, you have also a view of what is ahead to prepare yourself properly in advance when needed.
The only problem with that is that this is based on the wrong premises: what you must do.
I concluded that a calendar should not be a reminder of what you have to do, but rather an instrument to build the days you want to have. And this is important to live a satisfying life and be motivated to get out of the bed every morning.
One thing is let the world fill in your calendar, another more useful thing is to fill in the calendar yourself with things you want to do, and possibly filling it with something meaningful and useful so to make an effective use of your time.
So, my advice in this matter is to use your calendar as an instrument to build the day you want to have so to make the best use of your time and of your life.