Here is the comparison. The one on the right is the built in serpentine on the 6600 with a stitch width of 7. Default is 5 I think, and the length can't be made any bigger. The one on the left is the programmed serpentine using mode 2, stitch 14, with stitch width and length adjustments.
Basically you are programming multiple stitches with every stitch being the same stitch number, but with a different stitch width. Stitch lengths stay the same.