A Work or Cocktail Dress?

When I look at images of dresses such as the one above (left) from the YSL S/S08 show, my usual reaction is probably', 'oooh, that looks nice and structured.' But since it's not like I can actually afford YSL, my thoughts just stop there. It was until I saw similar highstreet designs that I started wondering where do people actually wear dresses like this to? The YSL dress looks thick (