The bungee cords and clips are for the sides of the quilt backing & batting to keep tension on it so it stays flat--no puckers. Leaders are for the top & bottom of backing & quilt top. If you look at the pictures of frames or quilts loaded on frames (machine quilting--not hand quilting) you'll see the 2 different things.
You unclip the bungee cords every time you advance/roll your quilt after a pass and re-clip after smoothing it all back out & before you start quilting your next pass.
There are all kinds of different ways to do the side tensioning. Bungee cords tied to clips--think potato chip bag clips--is the cheapest. I've also seen people make side leaders--pin those to the backing and clip them to a dress pants hanger which is then connected to a bungee cord and tied onto the side of the frame. Also cheap and useful if your backing fabric isn't quite big enough. Keeps you from bumping into the clamps with the machine so you can quilt all the way off the edge on a quilt that doesn't have a large enough backing.