Taken from Coach Randy Brown's site.
SET PLAY OFFENSE--ADVANTAGES
1. Coach has a large degree of control over which players take the shot. Set plays are purposefully designed for specific players to receive the ball in specific spots on the floor. Usually, that player is the one taking the shot also.
2. Execution is high due to the predetermined nature of set plays. Players know exactly where to start, what to do during the play, and how to finish the play.
3. During late games or special situations, set plays can be very good.
4. Coach can determine who handles the ball during plays to reduce turnovers.
5. Set plays take advantage of players strengths and hide player weaknesses.
6. Set plays can be called from the bench by coaching staff.
7. Set plays can focus on a 2-point basket, a three-point basket, or a need to penetrate.
8. Each set play can have multiple options. One play becomes six plays by reading the defense and taking.
9. Makes for a difficult game prep for the opponent because each set must be defended.
10. Set plays can be altered each year based on player strengths and skills.