Michael,    Does the scrap clay end up in  landfill?  While clay is   normally  innocuous and comes from the ground originally, clay still has bulk,  and our landfills are at the bursting point .   We potters are not  just unselfish purveyors of wonderful pots  but  we are often the  ones doing harm to the environment  in a variety of ways.    Not being sinless in this respect,  I can't cast the first stone....even if my main focus has been miniature pottery over the last 50 years or so!