Posture seems to be connected to the likelihood of injury in sports. ( **Journal of Orthopedic Sports Physical Therapy**
Posture can also affect whether food/drink is swallowed or aspirated. ( **American Journal of Roentgenology** )
Posture is related to fatigue for a person who is standing for a long period of time. ( **Surgical Endoscopy** ) (Incidentally, I can back this up with personal experience -- I teach, and the better my posture, the less tired and achy I am after a day of teaching. However, I figured I'd give the research first, since one person's experience isn't enough data for scientific evaluation.)
Posture can tell you a lot about the attitude, status, and interest of the person you're talking with. ( **Psychological Bulletin** )
Good posture can also affect motivation, stress, and mood. ( **Motivation and Emotion** )