It applies a Reflection map and sets up the reflection settings. Since the sheen on our skin is generally oily we will reflect buy only slightly. When doing realistic renders I always try to use Raytraced reflections, (true reflection if you like of the soundings) where as this setting use fake reflection via a reflection map. Look in the Surfaces Pane at the reflection channel and apply the preset..take another look…you can always use Ctrl + Z (Undo) or save your scene and play.