The video above demonstrates this technique. Due to the rates of fire that can be achieved by this technique, it is used by trick shooters and fast-draw competitors.
However, it must be noted that this technique may also damage a revolver's stop mechanism, especially when done very rapidly. One more point to be noted is that it isn't very good for shooting accuracy. There are only a few people that can shoot reasonably accurately with this method. That is one more reason why it is seen in trick shooting shows and not used very much by ordinary people.
Thanks to Hollywood movies, some people are under the impression that this was a standard technique used by cowboys in the 1850s. For an example, here's a scene from the classic western movie "Shane".
The technique of fanning a revolver was definitely known during that era, but the reality is that most real gunfighters did not use this technique in real fights, because of concerns of accuracy. What did real gunfighters think of this technique then? The following quotes are by one of the most famous gunfighters, Mr. Wyatt Earp, taken from an interview he gave later in life:
"In all my life as a frontier peace officer, I did not know of a really proficient gunfighter who had anything but contempt for the gun-fanner, or the man who literally shot from the hip"
"From personal experience and from numerous six-gun battles which I witnessed, I can only support the opinion advanced by the men who gave me my most valuable instruction in fast and accurate shooting, which was that the gun-fanner and the hip-shooter stood small chance to live against a a man who, as old Jack Gallagher always put it, took his time and pulled the trigger once."
"A skilled gun-fanner could fire five shots from a forty-five so rapidly that the individual reports were indistinguishable, but what could happen to him in a gunfight was pretty close to murder."
"Hickok (“Wild Bill” Hickok) knew all the fancy tricks and was as good as the best at that sort of gunplay, but when he had serious business in hand, a man to get, the acid test of marksmanship, I doubt if he employed them. At least, he told me that he did not. I have seen him in action and I never saw him fan a gun, shoot from the hip, or try to fire two pistols simultaneously. Neither have I ever heard a reliable old-timer tell of any trick-shooting employed by Hickok when fast, straight-shooting meant life or death."
These quotes and others are found in an authorized biography, "Wyatt Earp: Frontier Marshall" by Stuart N. Lake, where he gave a personal interview to the author about his life experiences.