Hi,
It is ancient and derived from examination of natural objects and dates to the ancient Greeks and Egyptians. Probably the Greeks, who idolized the beauty of natural forms promoted it the most effectively. Moving through time, it became a prominent guide during the early Renaissance when classic Greek art forms were rediscovered . But it is not a hard and fast rule for art. In a sense, it is the "null" model or "straw man" from which to measure deviations and differences. It is the basis for drawing correct looking perspective. However, an artist may want to deviate from correct perspective to create a statement or feeling. Think of the hundreds of great painters and sculptors who defied the rule to create feeling. Think about the feeling of movement and excitement in the carved scrolls by George Eister and John Noll. They don't fit the "golden mean" model but they sure look great and suggest life and movement. Often carvings adhering to strict golden mean proportions are static and dead. You've seen one and you've seen them all. A draftsman's or engineers idea of art. The golden mean is a useful guide to proportions and then go from there as your artistic soul sees fit. A word of warning , however, it is easier to hide within the constraints of golden mean proportions. Your design and work will probably look comfortable and pretty nice. It takes much more work to expand beyond it with much more risk. You can create a horrible mess unless you really have the talent to make your hands do what your mind sees.
dave
