I’m afraid that’s not right. The only 3D objects with a dispose() method are InstancedMesh (because of its internal instanced attributes) and certain helpers (because of their internal geometries/materials).
Just creating a group does not allocated disposable resources. The relevant entities are mostly materials, geometries and textures. Since they can be reused across 3D objects, you have to maintain their lifecycle by yourself (and thus call dispose() when appropriate).
Do I even need to dispose of the Box Geometries inside of the group in my example? I can say that, due to the program structure, it will only ever contain Meshes with a Box Geometry or a similar basic Geometry. Light and shadow helpers are delt with in separate functions, do I need to dispose of them too?
Is their a list online of all classes that require dispose and those that do not?