Maybe this is off, but I believe if the OS is competent and anchors the graft in the right place with the right tension, you don't need to hang weights off to get extension. Perhaps if the graft is too short, then yeah, they probably do want to stretch it to sort of make due at that point. I'm fortunate I came out of surgery and my leg was at 0 degrees and stayed that way ever since. I only do prone hangs off the bed in the morning because the knee is stiff when I wake. Then, it's only stretching hamstring muscles, I can feel that, similar to the feeling of when you do a figure 4 stretch.