The quilting is meant to stabilize and keep all three layers together. Zig Zag stitches are used on knit clothing so they can have some give and not pop the stitches when they are stretched. Different results are achieved according to how wide the zig zags are and how much space between each tip. So not really knowing the answer, I decided to Google "Can a zig zag stitch be used to quilt a top and the backing of a quilt?" Try it. It would seem the answer is yes.