I use "impossible" shaders a lot for illustrations. Please don't make my options limited.

Here is a visual illustration of the difference between the Blinn and the ks_microfacet specular reflection models.

Visualizing the subtle difference by brightness is very difficult. But transforming reflection amount into a displacement lobe makes it easier to see how they differ. Such displacement lobes are frequently used in the study of shaders.

Systems like LuxRender that declare these configurations impossible make them unusable to me.

If you want realism, then what you want are high-level nodes that do all the work - there is no reason to avoid adding such nodes. SM tried to offer this with the composite node, which would allow me to put together everything you need in a single box. However, they didn't do it right, and so the effort was wasted. That could be remedied. I'd like to see that remedied.

But one of the coolest things about the Poser material system is that realism is not the only thing you can do with it. Trying to judge which of those should be kept and which blocked is impossible.

Also, when people assemble "wrong" shaders, it's not usually because they plug things into displacement. It's because they don't understand physics at all.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)