Simple answer---you don`t benefit from it, which is why dryness /brittleness need to be held at bay by using leave-in conditioners and not shampoo the hair too often. Those scalp-oils can also interfere with bonding materials when you`re doing a re-bond of your system...a wipe-over of the scalp with an alcohol-soaked cotton pad will remove any traces of such oils and helps scalp hygiene too... then your tape/ glue can really grip the scalp-skin. A daily spritz with water and using a good leave-in conditioner or even a little Brylcreem onto / into damp hair will help mimic what happens when a person has all their own hair and it`s lubricated with the oils emanating from the scalp.