Sometimes (La Femme eyebrows, for instance) a mesh need to be hidden using a fully transparent material. Is there one node setup (pbr, vs poser, for instance) which renders faster?

A lot of times in Poser, I'm bitten by the fact that fully transparent does not mean no specula. A lot of times, I have la femme's hidden eyebrows reflecting light. So I turn the roughness to 1, specular color to black. emissive to black (even though it's set to 0 as a value). Fine.

But this left me wondering how the rendering engine treats that mesh. Is it smart enough to look at the values and say "drop these faces; they affect light not at all" or does it leave the faces in, run through the values, produce no affect on the face (but still do the math)?

Is a poser root better for this? Or a cycles root? This is using superfly. How does superfly handle faces with a node setup that produces no affect? And what's the best node arrangement for that?

Maybe some testing? But I was curious if I could get an answer from someone who knows how the rendering engine works.

there is a problem with SSS and transparencies that are close to the skin. The transparencies will glow. It's a known bug that they are working on.

I don't know the answer, but in principle if you used Cycles -- TransparentBSDF, that is unambiguous and there are no settings to tweak. Does that come with a performance advantage? No idea. It does probably come with a disadvantage in terms of how the preview looks, though.

Personally I've been using PhysicalSurface for this.

This won't help with other faces, but if you want to hide just the eyebrows, I have a morph here that will hide them until they fix the transparency issue

Cool, thanks. I guess for the eyebrows, since the mesh is completely invisible, I can "node" it into submission. But the morph is better.

I wonder if cycles is smart enough to know that the eyebrow mesh inside the head contributes nothing to the render and culls those faces during the render.