I can tell you that personally, my vocabulary has helped me in every aspect of my life. Personally, it helps me build relationships because I can understand and articulate my own feelings and experiences.
A good vocabulary helps me professionally. Not only was it useful in my teaching experiences, but now I work as a professional writer - a vocation in which it definitely helps to have access to lots of words!
It's even useful in my hobbies! I love to read and can read a variety of books because I have a solid vocabulary base. It also comes in particularly handy when I play word games and do crossword puzzles. It's really only a problem when I want to play Scrabble - no one in my family wants to play with me! ;)