What an excellent question. There are a few schools of thought about this one, depending again on the tradition within the Wiccan branch that one is associated with.

The scourge is a tool utilized to depict mental and bodily discipline, utilized to stimulate mental energy. It is also a sign of power and domination. Some covens use it purely in its symbolic form and others employ it for the means of opening their chakras through the stimulation of the feeling coupled with deep meditation/concentration.

Another avenue of thought, which could be hear-say, was that Gerald Gardner, who “uncovered” much of the underground Wiccan movement in the 1940’s, was said to have a penchant for whipping and bondage. Gardner had worked at one time with Aleister Crowley in a Ritual Magician’s Lodge and may have been influenced by Crowley’s need for showmanship with shocking the public. In magick there is sometimes a need to create a bit of sexual tension to generate the appropriate energy for some of the more mystical workings, which may have been a part of the reason it cropped up in some of the coven workings.

The scourge also was meant to bring about a gentle form of self hypnosis. Some practitioners found that the subtle but monotonous strokes, helped to affect their blood circulation as a means of gaining insight and focus. Despite its ominous look, the scourge is not used as a means to inflict harm.

Most covens that I have had the good fortune to visit utilized it merely as a symbolic tool, where the initiate was gently stroked but not flayed with the item; meaning that no pain was actually inflicted. In today’s modern Wiccan movement, it is not as prominently utilized outside of symbolism.