Originally Posted by
Prism99
I think the pressure setting (of the presser foot on the feed dogs) varies, so that on some machines the sewn edges get stretched as you sew. In this case, alternating direction has the stretched edges cancelling each other out. If you have a machine that does not stretch the edges as you sew, there is no need to alternate directions on the strips.
Probably too, some of the difference is dependent on how much the sewist pulls the fabric through the machine, vs. letting it feed through.