A golf ball with irregularities on its surface will fly further than one without (Golfwaterton.com or theannikaacademy.com). Wiliam Taylor made this observation 1905, watching pro golfers making scratches on their balls. He tested several patterns whereas the dimple pattern seemed to be superior to others. Most golf balls today have aobut 250-450 dimples (From Maddox Howe: Management of Sports and Physical Education, page 126.).
Record holder is the golf ball from Dimplit – branded Dimplit 1070. It contains 1070 dimples – 414 larger ones and 656 small ones (Armel Dawson: Sports Fitness and Training, page 233, Doug Lennox: Now You Know Golf, page 66). Dimplit golf balls are not produced anymore. You can still find images on Golfballs.com or buy one second hand hibid.com.
If a golf ball once has more than 300 dimples, the additional quantity on a ball does not affect the flight of the ball significantly, the dimensions and symetrical layout of the dimples get more important.