If one is writing a piece that includes informal dialogue, the usage would be entirely correct. In more formal writing, there are only a handful of contractions that should be used, but it is not the end of the world if less formal style creeps in, though if by chance context does not make clear which of two possible usages is meant, it can lead to confusion.
E.g. —Dorothy said “The world’s green—I think I’ll die of happiness.”
Does Dorothy mean that the world is green and she likes the colour [I write from Canada], or is Dorothy an avid golfer who has just hit a shot on the best green she has ever seen?
Ok thanks, now I know why I was taught to avoid contractions.