It's hard to go back and say what the original reason for dimples on golf balls was. But there's no doubt that they have a number of effects. One, as Sport Pilot said, is to aid in the generation of lift up or to the side through aiding the Coanda effect when a spin is imparted on the ball. However other factors weigh in as well such as the delay in airfow separation which is the real topic of this thread.