You can measure your quilt before staystitching. If the edge measurements are the same as the measurement through the middle, then no edge-stretching has occurred and staystitching will prevent the quilt edge from stretching while you attach the border.
Stay-stitching will not, however, prevent you from sewing excess border to the edge. If you sew with the border on top and do not use a walking foot, the presser foot will likely stretch the border fabric slightly compared to how the feed dogs move the underneath quilt top layer, resulting in excess border fabric being sewn to the quilt top edge.
If an edge measurement is larger than the measurement through the middle, then the edge has already been stretched and staystitching will simply prevent the edge from stretching even more; it will not eliminate the existing distortion or prevent additional distortion from the presser foot/feed dog difference.
Edit: OOPS. I think I got the presser foot/feed dog difference backwards. Must need more coffee........
Last edited by Prism99; 07-27-2012 at 07:27 AM.