I do no mark my quilts when free motion quilting. I do mentally plan my start and stop places so I don't have to tuck in ends of the thread if I don't have to. After a number of years of FM success and a few disasters, I am confident enough in my of skills to know how much quilting is enough. As mentioned before, to some extent it depends on the quilt. Somewhere I read about quilting in quarters. Meaning that you divide you piece into quarters mentally and deal with that amount of your quilt top. For me, that works beautifully.