Yes. The preferred seam for the backing is horizontal. If the seams are vertical when you mount them, they tend to distort the quilt sandwich as you roll it onto the takeup roller as the seam allowance on the vertical seam will build up. However, depending on the size of the table and the quilting design, the longarmer may be able to mount the quilt so the length goes horizontal. I sometimes do that as my usual quilting for myself is a free hand meander with extras thrown in. I don't have a computer on my longarm. Mounting the quilt along the length rather than width sometimes makes better use of my batting and also, I don't have to advance the quilt as often this puts the width on the belly and takeup bars. I have a 12 foot table so that is 144 inches minus the bit I need so I can access the bobbin.