The breadth of what a sound design can be is terrifyingly large - but so are it's possibilities.
The sound design for a musical may not seem much like the sound design for a play. But the final goal is ultimately the same - to help tell the story. The medium for one may be a high powered speaker system designed to deliver sound evenly across the audience - for the other it may be an orchestration that perfectly defines the time and place. While they require vastly different skill sets, they are both performed to help tell a story.