Quote - Maybe they're vestiges of a complex material setup the person keeps handy by leaving in, but with values set to zero or black so they have no effect?

See, that one I could buy.   I have material setups like that myself, like that blender setup I mentioned: it (potentially) connects to all the commonly used nodes in the Poser_surface, so if there was no reflectivity, or ambient, or alternate_diffuse, those bits of the node tree stay inactive.

But...

In those cases I have a single "switch" as it were.  To use the obvious real-world analogy, if I want to kill the power in one section of my home, if I turn it off at the breaker, going around and turning off all the lights and electronics and appliances one by one as well isn't  going to make a difference.