IMO, Cosby was behaving as a rapist so the crimes he perpetrated were not to relieve his sexual tensions but to reinforce his sense of power.
Therefore, when Cosby drugged someone so that she neither knew what is happening to her body nor what later happened to it, when the paralytic effects of the drugs prevent her from protecting herself physically, when the ill effects of the drugs cause her to be nauseous, when she has trouble remembering events, when she cannot match your financial resources, then his sense of power of women was complete.
He was, again IMO, performing an act of dehumanization. He was changing a vibrant, young woman into a mannequin who had no choice, no chance for objection, no opportunity to beg for mercy. He could touch her and, again IMO, by not mutilating or injuring her in some brutal way, he could actually reinforce his image of himself as being kind or benevolent or generous.
In previous posts, I mentioned how disturbing I found parts of Julia Leigh's 2011 movie, Sleeping Beauty, to be. The film is an examination of somnophilia or sleeping princess syndrome in a kind of case study of a young woman who becomes involved with people pandering to clients with that particular orientation. A young woman's willingness to participate in sexual acts was not a requirement. Rather, it was a young woman's willingness to sleep through someone's sexual or nonsexual use of her body, to awaken without knowing what happened as she slept.
I would imagine that in Cosby's case, he also derived some sense of power and satisfaction from witnessing his victims' confusion and fear when they "woke up", and when they realized that there was little, if anything, they could do to prove what he had done.
That man is one sick puppy.
http://www.theguardian.com/commentisfree/2013/aug/29/rape-about-power-not-sex
http://www.urbandictionary.com/define.php?term=somnophilia
https://en.wikipedia.org/wiki/Sleeping_Beauty_(2011_film)