From what I understand, the tulle or organza is used as an overlay to help hold down any loose edges. Mine are all fused, so I don't have any loose edges.
Danny Amazonas seems to do a zig zag around all his pieces, but Susan Carlson does free motion and uses the flow of the piece itself to determine where the quilting is going to go. I'm waiting for her book before I do anything. I did buy some invisible thread and I'm going to try Danny Amazonas' technique and see if I can do it.
Watson