I use a hoop quilting frame so I baste my quilts before quilting. If I get the layers straight when basting I don't have to constantly keep checking while quilting. I had a large quilt to layer and that is when I used the line down the middle to keep it all straight as I was basting using only an ironing board. I marked each piece and basted the line all the way down the sandwich first thing. No way the quilt could get all out of whack when finishing basting.