in my mind hitting the seams with a mallet would break down the fibers- i have seen it done though- a quilt shop demo a few years ago---we all kind of laughed --- and as far as i know none of us who were there for the demo actually practice it (but there could of course be some -closet whackers in our midst)
it just seems like it would break down the fibers and cause them to not hold up through laundering/use---but that is just (in my mind) i have no knowledge of the long term effect