I don't know if it is a must have, but certainly a nice to have. I only just got my mid-arm and am just learning, but I currently have a quilt in the frame that I plan do some straight horizontal lines and I think I would be able to keep them straighter with a channel lock. I know that you can use the needle down feature to keep the machine in place while you roll the quilt etc. but I am having difficulty keeping my straight lines straight. Everyone says it just takes practice, practice and more practice.