Sinbad has changed the comment on setVisible, it's now :
An alternative approach of making an object invisible is to detach it
from it's SceneNode, or to remove the SceneNode entirely. Detaching a node means that structurally the scene graph changes. Once this change has taken place, the objects / nodes that have been removed have less overhead to the visbility detection pass than simply making the object invisible, so if you do this and leave the objects out of the tree for a long time, it's faster. However, the act of detaching / reattaching nodes is in itself more expensive than setting an object visibility flag, since in the latter case structural changes are not made. Therefore, small or frequent visbility changes are best done using this method; large or more longer term changes are best done by detaching.
Just think of detached nodes as " large or more longer term invisibles".
I never suggested to make structural changes to the octree
