This article talks about the reasons why women have sex.  Men are obviously less of a mystery.  I haven’t read the book, but perusing the reasons offered in the article, it would seem reasonable to group many of the women’s reasons into categories of emotion management.  Sex appears to be a way to alleviate guilt (feeling sorry for someone), anger (revenge), or anxiety (pre-emptive protection).

In their new book, Why Women Have Sex,University of Texas psychologists Cindy Meston and David Buss aim to illuminate the complexities of women’s sexual motivations through women’s own words—an important step, they say, to better understanding how women can achieve sexual satisfaction. Based on five years of research and an online survey of 1,000 women, the authors consider motivation ranging from altruistic sex (”I felt sorry for the guy”) to revengeful sex (”I wanted to get back at my partner”) to palliative sex (”I had a migraine”). We hear from women who’ve had sex to boost their confidence, even if it’s with a man (or woman) they find repulsive, and from those who’ve used sex to barter for gifts or household chores (9 percent of us have used this form of economic sex, according to a University of Michigan study). We learn that 31 percent of women have had sex to evoke jealousy in the ones they love, while others have done it to protect themselves from getting hurt. Some, like the 25-year-old woman we described earlier, have had sex to boost their self-esteem, and 84 percent of women report they’ve done it simply to “keep the peace” at home.