|When you serge the seams of a garment and then turn the hem, the hem will be bulky where the seam allowance is doubled. If you clip the seam allowance where the hem will be folded, you can put the seam allowances in opposite directions and this will make a flatter hem. For example, if you are making a 1" hem, clip the seam allowance at 1" from the bottom raw edge.
This is especially helpful when using the coverstitch because a bulky seam often gets hung up under the presser foot. Even with the seam allowances in opposite directions, my serger (Babylock Evolve) struggles. I keep an awl handy and use it to help the seam get past the needle.