"Communication is one of life's most important skills"
I’m prejudiced with regard to writing as a retired Foreign Service Officer at State where vanity about writing skills was rampant, but I agree that writing is one of the best ways of learning a subject and framing what you think about it. The effort and energy involved in explaining something to others inevitably leaves you understanding it better yourself. One of the best military writers I ever knew was a USMC Major in my seminar group at the Naval War College.
Writing has many purposes: to inform, to direct, to influence, to pursuade, to inspire, to enable, etc. All of these are productive and important at different times. The beauty of writing for publication is the fact that it can reach a broad audience and become available for generations to come (if distributed and archived well).