This chapter felt incomplete and unsubstantial after the rest, like we crested a massive hill in Part IV and V, and now we're on the downside. Which is not what one would think when reading a chapter on sex.
In a nutshell, yoga can improve the quality of your sex life. It does it through the manipulation of testosterone.
Simplified? Oh yes, but that's rather what I pulled out of this. It seemed there was so much focus on the chemical aspect of yoga affecting sex, that it didn't at all take into account that a) people who do yoga tend to lead healthier lives, and b) if you are leading a healthier life, then generally your sex life is going to be better and c) yoga makes you calm and if you are calm, your are going to be more receptive to your partner, etc.
This chapter discussed at length the role testosterone has in doing yoga, it touched on a handful of poses that are known to stimulate our base desires and discussed at length the Kundalini practice.
I have to say, I started to lose interest. Not my favorite chapter.