I'm not sure about other machines but its not really a good idea to drag fabric over the feed dogs in all directions if they are trying to do thier job of 'front to back'.
So says my engineer for Bernina 180 (about 10 years ago)
Makes sence to me!
Oh! and I am hoping to pick up a walking foot when I visit England next month :) Never had one before!!! Been saving up the £75 to pay for it!!!