The romantic and sexual side of Couchsurfing is a byproduct of the intimacy that results when two people share such a close space and of the ethos around travelers in general.
There are a wide variety of people, of sexual preferences, of relationships styles. There is value in a fling, and there is value in finding someone who pushes your sexual boundaries and exposes you to new pleasures you didn't know possible. These are not one-time, throwaway lessons. Rather, these lessons are carried with you throughout your entire life.