The major problem with the single Carabiner Wrap is that there is not enough friction with one wrap, and not really enough room in the carabiner to add a second wrap without bending the rope sharply. The three carabiner wrap method solves these problems in a manner that is too complex for many people to remember.
If you look at the picture, you will see note several things:
When rigged as shown, the top carabiner starts with the gate toward the rappeller, and although the rope tends to rotate it to one side, this is the safest direction. The lower carabiners are closer to the rappeller, and less likely to hit the lip accidentally. Locking carabiners should be used.
This rig seems to have about the right amount of friction for my taste. Obviously more friction can be added by extending the chain to four or even five carabiners. No matter how many carabiners are used, this method does introduce significant spin on free drops.
Do not use this method without locking carabiners.