Visioning. Helps you envision your future clearly and allows you to create a roadmap on how to get there.
Goal setting. Writing down short-term goals that help you keep on track with your vision.
Retaining what you read. I don't know how many of you can relate, but I have an extremely hard time remembering what I read sometimes. It's not due to lack of interest in what I'm reading. I believe it's because I have so many inputs coming into my brain on a daily basis that it makes other tasks, like retaining what I read, very difficult. Writing and re-hashing what I read makes it easier.
Remembering everything at the grocery store. Helps you be efficient with your time while at the store, ensures that you don't forget anything, and helps you with managing your health.
Tracking progress with your fitness routine. How else would you know how to progess week-to-week and training block to training block?
Perhaps the most important thing though, is it reinforces critical thinking. If you ever get a delayed response in an email from me it's because I need to critically think and give you the thoughtful response that your email deserves. These are emails that require a nuanced response. Emails that I can't answer in 30 seconds or less.
As we get older, I believe this becomes of more and more importance.
Put a pen to paper (or fingers to a keyboard) and start writing.