When drawing an object (eg sending draw calls to the GPU) the object boundary sphere is tested against the active view). When the test fails the object isn't send to the GPU. Before this happens the GPUBatches were already generated.
When doing animation playback this could lead to the situation that the GPU Batches are calculated, but not used.
When using the Overlay engine/Workbench engine we could test the objects to the default view (e.g viewport). When this fails we could skip this object at all. This feature would be disabled when the shadows are turned on and only enabled when doing an image/animation render.
A consistent framerate is more important to animators then having some frames faster.