Some of the videos show lowering the top tension on one of both threads (if you have a two tension machine) so that you get more of a straight appearing stitch on the back. So then you'll get more of a "line" look on the back.
I have a double needle machine with two tension dials, so I can balance one thread with the bobbin tension and have the other one significantly looser. I also have a hemstitcher with two needles and two bobbins, and will do a double row of stitching if the piercer is removed.