"[A cocktail party] is a sort of unorganized receiving line, in which many women enjoy greeting all their friends and acquaintances once a year or once a month." (pg. 24)
For most of us, cocktail attire is also a pretty easy dress code to abide by. We don't have to worry about the hassle of finding a floor length gown for a black tie event and we aren't left wondering just how casual is casual. The Little Black Dress with a great piece of statement jewelry is the easy outfit option, but you can also pull off a pair of ankle pants or a skirt with a silk blouse. Most of us aim for the "dressy, but not overdressed" look and luckily there is a lot on that spectrum that is appropriate for a cocktail party.
Madame Dariaux doesn't exactly agree with me.
"The perfect hostess wears a dress that is only slightly décolleté, or not at all, but of a rich material...The dress worn by a guest at a cocktail party should be scarcely décolleté at all." (pgs. 24-25)
Since the stark lines between dress codes for events have blurred (at least for the many of us), we are given more options in attire for semi-formal events, like cocktail parties. This means that no matter your body shape or your personal style, you can find an ensemble that makes you look and feel elegant.
Dariaux, Genevieve Antoine. A Guide to Elegance. New York: William Morrow, 2003. Print.