The key to great decorating is mixing a few different styles into a room. This gives the room character and contrast. It also keeps a room from looking like you went to the store and bought everything from the same furniture line...a feeling of collecting pieces over time.
You may also love 2 or 3 different styles and don't want to have to choose. I love the look of a modern home but often feel like its too cold for everyday living. This is where adding traditional elements into the room can make it feel more warm and inviting.