Yes, they definently can be louder than a ported box //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
Advantages?It gets louder over a wider bandwith if done properly.Increases mechanical power handling
Disadvantages?Some people don't like the sound, but most that say that have heard a poorly designed/constructed bandpass box.But the main one is space.These boxes are typically very large.