I was taught by my first quilting teacher to miter all borders and bindings. Fast forward many years ... now after reading many of Gwen Marston's texts, I am reminded of how different things are since our ancestors sat rocking and sewing quilts by hand.
Did they miter? According to Gwen it's the rare antique quilt that has been found to be "mitered." I think, much like the Amish say, it would have been considered wasteful and too "fancy." I used to miter, now I rarely do. I would include another reason not to. It's more time consuming for today's minute conscious quiltmaker. Our quilts are beautiful whether mitered or not. 8-)