I think it was important before the inception of reliable birth control, in a patriarchal family structure. Before birth control, if women just slept around then we wouldn't have the nuclear family unit, which is major facet of western civilization
However, in today's world, there's no real reason to shame women for being promiscuous if they are using protection. It serves no function as society does not benefit as whole because a woman is chaste. If anything, unprotected sex with someone that you are not married to is the only thing that should be shamed, if we want to follow the existing model.
However, although most women will disagree, I fully believe that "slut shaming" and the encouragement of male promiscuity has way more benefits than drawbacks for women. The supply/demand table heavily favors women in terms of sex and dating in general. This gives women a strong advantage when it comes to dating and sex. There's a reason why fat women can sleep with good looking guys, and slut shaming is a big portion of it. Women tend to not acknowledge this, tho.