Why own a black leotard? Because it is a garment with many uses. It can be worn under your clothes, revealing it just a little under a blouse. It can be used as a top, or it can be used as part of a costume. If you were to make your own Playboy bunny outfit, you could use this type of leotard. The original actually uses boning like a corset would, but for the sake of comfort, you may opt for something less rigid.
Here are a two versions – both very basic, but they do the job, I guess:
Black strapless leotards pictured:
Left: Dreamgirl Black Leotard Adult Costume
Right: American Apparel Cotton Spandex Jersey Strapless Ruched Bodysuit
Of course, leotards are also dance-wear.