1. To increase her satisfaction with the relationship, and therefore minimize the risk of infidelity.
2. Sperm retention; the study notes that previous research has found that women retain more sperm when they orgasm shortly after their partner's ejaculation. They apparently retain more sperm in this way because a female orgasm has been shown to cause uterine contractions, 'which pull sperm further into the reproductive tract'. According to the study, this could be why performing oral sex on women is evolutionarily beneficial, since the retention of sperm promotes conception.
Ladies and Gents, do you agree with the outcome of this survey?