Bonnie Hunter's (quiltville.com) theory on leaders and enders is that if you keep scraps near your sewing machine, you start with 2 pieces of scraps and sew the 1/4" seam (leader). Sew your project block, then finish (ender) with another scrap. You don't use the same scraps over and over. You keep going with this method so that over a period of time, you have blocks starting to form for another quilt.
I believe the main intent is to have actual blocks for a quilt ready to sew and make these your leaders and enders. Then as you work on one project, you are actually working on two with the leaders and enders method.
Bonnie makes scrap quilts and think this is how she came up with this idea. I keep scraps by my sewing machine and do this then square them up into possible blocks for scrap quilts.
Hope this makes sense.