I agree the big advantage is that using leader/enders is that you do not have bits of thread to trim and discard constantly. And...you get through tedious tasks easily over time.
I have one friend who cuts all her scraps into 2" squares and keeps a basket of them at machine side. She just stitches two together every time she ends a seam and leaves them under the needle.
I like to make 8 and 16 patch units so my leaders/enders are strip sets (from which 16 patches eventually emerge): I cut a 1" strip and a 1 1/2" strip off every fabric I buy and put those strips into baskets. I sew two strips of the same width together as a leader/ender. They go into another basket and....then I sew two sets of those together. And so on!