The confusion could be caused by the way the material editor displays material layers, which are really just naive material functions. Because the material attributes node isn’t aware of the shading model, it makes it appear as though every input is available to use by leaving all of the pins open.
Whereas it’s evident when directly editing a material and displaying the inputs normally that many inputs are, in fact, discarded or dependent on the material’s ultimate choice of shader model (e.g. metallic is disabled by the subsurface profile model, and is changed into ‘Scatter’ by the hair model). Even some input nodes, like light vector or scene color, are only applicable to certain shading models or blend models or material domains.
Speaking of which, rendering a pixel multiple times isn’t that much of a deterrent because the translucent blend model necessitates it. Clearly the performance hit can be worth the price if the feature is important enough.