Quick Spin Kick, called Quick Sobat (クイックソバット kuikku sobatto) in the Japanese version, was introduced in Tekken 2 as part of Bruce Irvin's moveset, then returned in Tekken 3 as part of Bryan Fury's moveset in Bruce's absence. There were slight differences in the moves, however, as while Bruce's second kick would launch the opponent, Bryan's would not.
When to use (Bryan Fury)
While the Quick Spin Kick may have a use as a stand alone move occasionally, it's real value is in the moves it can chain to and from.
When to use (Bruce Irvin)
Bruce's Quick Spin Kick's chain moves aren't as diverse as those of Bryan Fury's, so it has more use in juggles.