I totally agree with ernyoka1. Mine was just a quick way to use something instead of nothing and have some better results than with the original skin texture. But, there are drawbacks: think to a skin with tanlines... that would cause bumps where they are not supposed to be! So sometimes a simple noise node (tweaking the settings by trying) could be just fine for giving the surface some grain. And the displacement maps, well, those can dramatically change your geometry in the render (too bad you can't see the effect till you actually render, not me at least...) Happy experimenting!