The diffuser does many things. It breaks up the bubbles so you get lots of smaller bubbles instead of a few big ones. This usually results in a thicker smoke. The diffuser also quiets the bubbles a bit. It also reduces foil rattle (as I call it). Foil rattle is when the foil shakes and vibrates when you are drawing in smoke. This happens alot with a Nammor hose and small Super Chief bowl due to the big bore. Foil rattle is a pain because it vibrates you coals so you have to watch they don't fall off.