Golf ball dimples were first discovered somewhere around 100 years ago when some golfers noticed that balls that had been scuffed up or scratched traveled further than the new smooth ones. It's from there that golf ball dimples were born.
What do they do?
They allow the ball to travel further up in the air producing what is known today as lift (forcing the airflow downwards that in turn pushes the ball upwards).
There are no limits to the number of dimples that are allowed on one golf ball with average being somewhere between 300 and 500. What are really important are the design and the dimple pattern on each ball.
This directly impacts the balls trajectory, flight pattern and distance. There used to be a myth that the more dimples that you have, the further the ball will go. That has been proven not true.
The amount of surface area covered by the dimples and their specific arrangement are what affects the golf ball aerodynamics. This somewhat simple finding has become a true science that golf ball manufacturers study in detail to try and create the ideal combination. This includes the size, depth, width, shape, number, and pattern. They say golf is a game of inches; well it's actually 1000ths of an inch when it comes to dimples. It has created a huge market of competition to create the perfect golf ball.
What actually happens?
Well, the manufacturers are trying to accomplish a few things during golf ball design. First they are trying to minimize the drag forces (pull back or slowing down) of the ball. Second they are trying to maximize the lift and the angle or trajectory from which the golf ball travels through the air. All this plus taking into account the type of ball, the core, and the cover to name some other outside factors.
Golf ball dimples allow the airflow to follow the outside surface of the ball while reducing drag forces and creating spin for better control and a more consistent flight path. They golf ball flies on the same basic principles as an airplane. As stated earlier the air passing by the ball is forced downward which forces the ball to go up.
Since there are no real formal rules from the USGA concerning dimples you will see all different types and designs. This gives the players a choice to find the perfect ball with a dimple pattern that gives them the ball flight they want to achieve. As new balls come out onto the market the players have to try them out to see if the new technology gives them what they desire.