I've got mixed feelings on this. I could definitely see the benefit of an all women's class if there are religious restrictions in the community against unrelated male/female contact. I think it would also be a welcome thing among women who are very body conscious, either because of being overweight or because they have "perfect" bodies and have felt uncomfortable being in close physical contact with guys who find them attractive.
Fortunately, however, I'm old, ugly, and dumpy and fine with that, so I don't mind being in mixed classes at all.
In fact, I prefer it since I don't care for the social dynamics that can sometimes arise in an all-female group. I've never been made to feel overtly unwelcome by anyone because of my gender, and usually ignore the one or two jerks that crop up from time to time.