I keep my shader trees pretty simple, mainly using textures to modify the various channels.  That means I rarely use more than one node per channel.  I've compared renders with and wihtout disabling shader nodes and the results were as I expected.  Turning off the nodes I had no bump maps, and the transparencies seemed different.  Turning them back on gave the results I wanted.  I assume it was because I'm using textures and not procedurals.

I've never thought of rendering anything that high until a few days ago.  It must take ages!