Which old builders said that one should hold in the air button at all times during a song? In order to prevent breaking reeds?? Perhaps that person knows how to build accordions, but as far as playing them, I don't know.
If the player was meant to have a constant leak in their accordion, then all accordions would come with a leak.
In order to prevent breaking reeds, don't play so loud!
True, using the air button when your very far out with the bellows will prevent you from pushing in too hard to come back (as well as sounding your reeds unnecessarily too LOUD), and in turn, will keep you from busting all your PUSH reeds....
However, that part about pressing the air button throughout that whole song is gross misinformation.