My mom used to do that, too- winding open color thread on top of another. It never made sense to me, especially if you needed the underneath color and had to unwind thread to get to it. I'm not sure saving everything is necessarily good. It seems rather useless unless you can find it, or you'll spend a huge amount of time (wasted) trying to find it. I'd rather throw out a few yards of bobbins thread unnecessarily than have 50 little containers with odd bits of thread clogging up my sewing area.