I think I remember reading that FW dips were reccomended when the "pinched mantle" problem was happening with a lot of clams all over the place. I've never seen it reccomended otherwise, never tried it myself. I haven't seen anything about "pinched mantle" reccently.
Were you thinking FW dip as a preventative for "pinched mantle", or for other concerns?
Maybe you could post a question in the Clamsdirect.com fourm (if it's still up and working) and see what you get?