Spheres are the "hello world" shape of ray tracing, but are generally not used for production renderers for the following reasons: Spheres are not that interest

Spheres are the "hello world" shape of ray tracing, but are generally not used for production renderers for the following reasons: Spheres are not that interesting to render, because hardly anything in the real world is a perfect sphere; and determining a ray-sphere intersection point requires solving at least one quadratic equation, which requires a square root, which is slow Triangle meshes are better choices for the same reasons: they can be used to model arbitrarily complex shapes, and it's faster to compute ray-triangle intersections.