I don't hunt from a treestand much, however I use a safety harnesses at work. #1 rule is a safety line is only good if it prevents you from falling off or hanging mid air so you can't get yourself unto stable footing. #2 is the harness should be a 5 point harness which distributes the force of the fall and pressure to your legs, shoulder and torso. I'm not up on the new harnesses but basically you should step in to leg holes, pull over the shoulders and belt across the chest. Safety line hook in should be between shoulder blades. The harness must be snug enough not to slip but obviously not to snug to be uncomfortable. #3 safety line hook in point is situated so if you do fall it will hold and be in a direct as line as possible to decrease tangling or miscalculations and falling further then you intended(not as much of an issue for a treestand, since I assume most hook in directly behind their seating area but I've seen some shows where they have the line off to the side and that could present some troubles if they went off that way_

I have a sliding hook up on my safety line to allow me to move and work around the area, I cinch it in so that its pulling me well before I'm in any real danger. I've had a couple really close calls when getting to cute with my pressure points and actually learned from those expereinces. Basically if your at the edge and its not yanking you back hard, your too loose. In the woods your by yourself most times and need to be able to bail yourself out vs count on some one to help.