Effective communication, both written and oral, is essential for (most) careers in that it allows you to effectively articulate what you a. want b. need c. have found to be true d. would like to see happen.
I'm a former teacher and a third-year law student. I work regularly on written legal memos on environmental issues. I also have to go in and explain those memos. Without written and oral communication skills, the people that I am working with will have no idea what I believe or have found to be true on a particular matter.