Easy and actually fun to use. Create perfect arc animations for clips in FCPX. The clip’s center is *always* on the circle used as the guide. The “pole” marks the center of the “universe”. When keyframing animation, setting all positions and rotations back to 0 brings the clip “back home”. Easy.
You can also reverse clips (flip image) to utilize front side of circles—you’re not limited to just the back side. You have control over the reflectivity of “the floor”. You also can eliminate the floor altogether by setting the Floor Designer opacity to 0.