When adjusting a standard camlock buckle on most standard weight belts you have to release the buckle, therefore with your weight belt no longer securely attached you pull the webbing tighter whilst trying to keep the belt on so that the next time you flip the camlock over to lock it back into position you hope that you've pulled the belt tight enough for a more comfortable fit.
Quick release weight belts allow you to adjust the tension without having to undo the buckle. This ensures the belt is securely attached to you! In other words you can adjust as necessary (i.e. when your dive suit compresses) without loosening or undoing the buckle. Another nice feature is the total absence of flapping around weight belt webbing.