Turning edge of crochet...A lot of beginners (or those of us who don't like to count) increase or decrease when turning. Marking the last stitch of the row keeps that from happening. This will show you what loops form that last stitch and need marked. If you're wondering, the stitch I'm using is half double.
Also on these boards
where had this been all my life??? short video showing alternate double crochet turning stitch - instead of ch3. makes a clean edge.