Physics Collaborations

Here is some code from the manual to show physics setup:

node = NodePath("PhysicsNode")
an = ActorNode("jetpack-guy-physics")
anp = node.attachNewNode(an)
jetpackGuy = loader.loadModel("models/jetpack_guy")

I’m confused about why so many different node-based elements are needed for this process. I know the ActorNode is what the physics actually acts on, and since you add nodes to NodePaths we get the anp (ActordNode path) to add the jetpackGuy. Whats the purpose of the first node path “node”? Why not just add anp to render and cut 1/3rd of the nodes out of there?