Further from the camera, the coordinates are larger and thus more expensive to compute on. Also, there are more things further from the camera, even though they are all smaller. Thus, it's practical to just eliminate any primitives partially outside the frustrum cube.
Further from the camera, the coordinates are larger and thus more expensive to compute on. Also, there are more things further from the camera, even though they are all smaller. Thus, it's practical to just eliminate any primitives partially outside the frustrum cube.