Everyone likes a good sturdy heel flap and gusset but quite often there can be gaps where you pick up stitches along the heel flap. The slipped stitches provide a great line to follow when picking up the stitches but they can be a little loose. But knitting them through the back loop on the next round helps to tighten them up a treat and gives a good solid heel flap which will be hard wearing and hole free.
