If you are sewing ties together for a skirt, for example, you may want to stabilize the seam lines to avoid stretching the fabrics.  Cut the pieces needed and measure the length of the raw edges to be sewn.  Cut 1/2" wide strips of fusible underlining (HTC's Touch o'Gold II is what I use) and fuse centered over each seam line on the wrong side.  Sew seams.  Your skirt will still drape nicely, but the seams won't stretch as you sew.