When you write something down, it stimulates a bunch of cells called the Reticular Activating System (RAS) that exist at the base of your brain. The RAS filters all the stuff that is going on at the time in your brain and gives more importance to the things you’re actively focussing on at that moment. Writing something down brings that information to the forefront of your brain, making it more likely that you’ll remember it.
This doesn’t work though for typing as when you write using your hand, you activate more of your brain and are thus able to remember better.
As to leadership, let me pose a question. Is there anything you have learned about being a leader that you have actually written down?