no description available, TAbstractGeometryNode description follows
Geometry nodes are the only nodes that produces some visible results during rendering. Much of the VRML language is just a method of describing properties how geometry nodes are displayed (materials, transformations, lighting).
Only geometry nodes define something visible "in usual way" during rendering (Some other nodes in VRML / X3D are visible but in an unusual way, like Background and Fog. These nodes must be rendered in a special way — they are not affected in any usual way by the current transformation matrix etc.)
Geometry nodes are never "grouping nodes", in particular there's never a geometry node that is (direct or indirect) child of another geometry node. So there's no need to be concerned whether geometry nodes' children are included in things like [Local]BoundingBox or Triangles/VerticesCount.
Geometry nodes don't affect anything in graph traverse state. (This is important mostly for VRML 1.0, since in newer VRML / X3D "graph traverse state" is not that important.)