Complex sentence: Images can be delivered at the same frame rate regardless of how big the 3D data was that was used to generate them, so performing 3D rendering on the server effectively converts the 3D performance problem into a 2D performance problem.
Split into simpler sentences: Images can be delivered at the same frame rate regardless of how big the 3D data was that was used to generate them. So performing 3D rendering on the server effectively converts the 3D performance problem into a 2D performance problem.