I love to use the decorative stitches on my Bernina when machine quilting my Linus quilts. It gives a little extra flare and like someone else mentioned in makes quilting in the ditch much more accurate. I also believe it helps hold the piecing together. I like to use varigated quilting thread as it also looks more decorative. I use a walking foot if I am quilting. The decorative stitches really dress up any sewing project. We have those small memory foam pillows on our bed. I made pillowcases for them as the queen size ones that came with my sheets are way to big. I used a decorative stitch about 4 inches in from the opening just to make the pillowcases look a little special.
For anyone who wants to participate in the " one million pillowcase project" you could decorate a store bought pillow case with embroidery, decorative stitches or some appliqued motifs etc. I do something like that for my grandchildren and great nieces and nephews for special occasions.