I think it depends on the situation. I would say, high school, college girl in a non serious relationship, better not. Why? Once word gets around you're 'easy' there may be guys who take you out for no other reason, which is a bad thing, unless you are someone who honestly 'wants it' like a guy and doesn't mind being used. But I do believe this leads to using of girls' bodies and I don't like that. I feel like any young virgin should be very picky over who, when and where she gives herself to a guy. It's a decision that lasts a lifetime.
On the other hand, older girls, late 20's-30's who have not been married and are seekng serious relationships and want to 'try out' before commiting, well, that's up to you. Divorcees, or those who have already been in long term sexual relationships that failed, why not. Having known many females who were on another go around after a bad situation, I don't see anything wrong with living with the guy to see how it's going to go. In some cases it's the smartest thing to do.