Are objects protruding out from the scene actually rendered or computed(gpu,cpu) even though they are invisible to the player?
If an object’s bounds intersects with the camera frustum or the cone of any shadow-casting light (there are probably more cases than those), it must be at least considered for rendering/processing of some sort even if most (or all) of the object is invisible to the player.
From what I’ve gathered, it’s a good idea to avoid having meshes with huge dimensions - better to split them up into smaller pieces (fast culling happens on a per-object basis).