the Principled shader is a way to group the other shaders into a work unit (for those who don’t understand or don’t want to be bothered with the tech side)…
it doesn’t take (for instance) the glossy shader out of the mix but rather puts it in a useful place in the pipeline…
so the shaders get incorporated (they are always present) into the grouping
that is commonly referred to as PBR (Physically Based Rendering)…
hope this helps…
😀