Some decorations can tell as to what the situation is. Let's say the decorations for Christmas can give you a clue that Christmas is around the corner. The same for Halloween or Thanksgiving.
People see decoration as just something they have arrange to spice up the event or to show their talent in arranging and making an event colourful.
However, decorations should say what we have in mind concerning a gathering. It is usually nice to see a good decoration in an event.