An analytical ellipsoid is derived from an ellipse by introducing a third axis 'C'.
When all the three axes have equal lengths and they are perpendicular to each other, the shape is a sphere.
The sphere supports an efficient inside / outside test, which makes it especially useful object in Boolean operations. It is also very quick to render in ray tracing.
An ellipsoid doesn't support Sector attribute. If this option is needed, use an Ellipsoid Segment object instead.