The reason why golf balls have dimples starts with natural selection.  Originally golf balls were smooth, but golfers noticed that older balls that were beat up with nicks, bumps and slices in the cover seemed to fly further. Golfers, being golfers, naturally gravitate toward anything that gives them advantage on the golf course, so old, beat-up balls became standard issue. At some point an aerodynamicist must have looked at this problem and realized that the nicks and cuts were acting as "turbulators" - they induce turbulance in the layer of air next to the ball (the "boundary layer").  In some situations a turbulent boundary layer will reduce drag.