I generally piece my borders but I hate really short pieces. I prefer my pieces to be longer. Since I need at least 2 pieced borders, I cut 3 strips WOF and sew them together and split the entire length in half. Then I can trim it the way I want. The extra pieces go in the scrap bin or they can be used in back art.
I forgot to mention that it is important to pay attention to the placement of seam lines when doing mitered corners. You do not want a seam in those because the miter already ends up seamed.