You have to secure the poly batting so that you can trim it prior to sandwiching your quilt. You don't want to use regular thread for that. So you aren't thinking through that you will be trimming. If you used regular thread for that set, then trimmed, then stitched...you would either have to take out the first stitch lines, or you would have a double row. I'm not good enough to do it twice and hit the same holes. This way...it doesn't matter.