As an example, take geometry culling. That can save bandwidth because the more you cull, the less work you have to do. On the other hand, culling is not free. It takes compute resources to check if a triangle is hidden behind another object. If the triangles are small and numerous, that's a lot of checks, and many of the checks are going to decide "Yeah this triangle is visible" anyway. So in some cases, it's better to just ignore some of the extra checks to avoid that overhead, and take the hit on more processing later.