Collagen sponge in crestal sinus elevation: why and when to use it?

The colleague’s question

I saw italian doctor after sinus lifting, they then use some kind of spongy membrane inserting into the osstetome then futher mallet. Plz share your protocol Why we use spongy before breaking the sinus. I think they use the spongy acting like a cushion avoiding direct contact to sinus membrane in some case