The frequency of nocturnal emissions is variable, just as with males. In 1953, sex researcher Alfred Kinsey found that nearly 40% of the women he interviewed have had one or more nocturnal orgasms or wet dreams. Those who reported experiencing these said that they usually had them several times a year and that they first occurred as early as thirteen, and usually by the age of 21. Kinsey defined female nocturnal orgasm as sexual arousal during sleep that awakens one to perceive the experience of orgasm. 
A good orgasm for a man is the sexual equivalent of a cold beer at the end of the workday: a satisfying reward for a job well done. The job in this case is pleasing you. A major part of the satisfaction men get from sex is the ego boost that results from making our partners go bonkers in bed.