My guess would be trouble keeping the seam allowance 1/4" all the way across. I tend to be less attentive toward the end of a strip. I don't think the short length of a coin would distort that much if you sewed all from the same side. I'm sure I sewed the ones for the back of my Carpenter Star all from the left to right. I did strip piece them, so that cut down on that slight curve at the end of a seam.