An AAV can significantly decrease the amount of venting material required in plumbing system. That is money in the pocket for the plumber. They also permit amazing flexibility in the layout of plumbing fixtures, and can decrease long-term roof maintenance where a pipe vent roof penetration was eliminated during the design process with an AAV. One less hole in the roof, one less hole to maintain in the roof. AAVs have been used in Europe for more than 2 decades. However, there are restrictions.