Things that are decorative have no purpose except to look pretty. Blueberry bushes produce fruit that humans and birds can eat, while boxwood shrubs are purely decorative.
The fake buttons on your winter coat are just decorative — then again, your high heeled shoes are more decorative than useful, and your jewelry and makeup is also decorative. The knickknacks on your mantel, the wreath on your front door, and the creepy doll collection in your living room are all decorative as well. These things dress up or ornament your home, and decorative comes from the Latin root decorare, "to decorate, adorn, or beautify."