My 2p is that reading, whether words or music, seems to interfere with most folks abilioty to listen to what the other participants in a session are doing. Maybe its like trying to walk and chew gum at the same time. Without being a purist or overly dogmatic, we make a subtle effort at our session to have a "learning segment" toward the end of the session, during which holding the paper is tolerated with a bit more grace. The one reality about the folk process is the fragility of absolutes.