This method of shaping allows the closest physical contact with the hot glass. This close physical contact allows the glassblower to get a "feel" for the glass. The neck area is chilled and shaped first, then the wet paper is used to shape the piece. By having an assistant blow while the bubble is being papered, you can get the bubble to expand in areas you need it to, and prevent it from blowing out in those places where you don't want it to. This can be especially useful when trying to blow out the shoulders - you paper the bottom while your partner blows to expand the bubble and shoulder area.