I do not piece my borders. Also I sew the outside large borders strips together end to end and not on the diagonal. That wastes a lot of fabric and you can not tells how the borders are sewn after the quilt is quilted. I do however sew my inner smaller inner borders diagonally.! have tried sewing the outer borders on the LOF and actually saw no difference. By sewing them that way the outer border is not supposed to be wavy.
remember- there are no quilt police!!!!!!!