This iExpression changes the meaning of the x, y, and z value of the property such that you can easily animate it along a sphere surface. Technically speaking the iExpression turns your coordinate system into a spherical coordinate system. Simply speaking, you can animate the property via keyframes as usual but the values have a new meaning: Applied to the position of a layer, the x and y position now do not move the layer left/right and up/down anymore; instead they move the layer along the surface of the sphere. The radius of the sphere is given in the z component. In order to orient the layers correctly on the sphere surface, apply the "Look At Point 3D" iExpression to their orientation and choose as "Look At" point the center of the sphere. If you want to move or rotate the sphere, its best to set the center to (0,0,0), then create a new NULL object, make it 3D and parent the layers on the sphere surface to this NULL. During the parenting, keep the alt or option key pressed. Then the position of the NULL becomes the center of the sphere and you can move or rotate it using the transform controls of the NULL.
is the center of the sphere along whose surface the property is moved.
Scale Radius (%)
allows to scale the sphere. If the x y and z values are not identical you obtain squeezed spheres (i.e. elliptical ones).