To me, the saber fanning out and such, seemed like it was made to intimidate the opponent and make them step back, or if they attempted to attack, the spinning saber would probably knock the attacking saber away, and leave them open to attack.
Now when I saw both of them use it at once, my first thought was that it had to be a technique one of them made (probably Obi-Wan), and shared with the other one. I thought the whole point of it was to show that they were extremelly alike as far as knowledge of the saber went, since they were master and apprentice. The fact that they both stopped at the same point in the fan just reemphasized this.