I have been sorting my second haul of LEGO pieces into sets recently. So far I have been able to identify roughly a hundred sets from that pile and there are still some pieces left. The problem is that even though I'm fairly certain from which sets some of those parts are there are so few bricks left they wouldn't be enough for some of the remaining sets even if all the remaining pieces were from a single set.
Most of the sets have had at least some pieces missing. So I don't mind if those remaining sets wouldn't be complete either. But what's the point when you realize there are more pieces missing than there are pieces available for a set? I could as well leave those pieces as spare parts for the next lot.
But I'm a completionist. I would really find a home for every piece of LEGO I have instead of having some left over random pieces hanging around. Even though I did so with the first lot I don't either want to mix the leftovers with the next one. It just leaves me wonder where does this piece coming from when I'm again nearing the end of that pile. I could as well keep them separate and just check for any missing pieces after I've gone through the lot (and left with another set of pieces without a home). But then I would need yet another set of containers to keep those pieces as I don't want to mix them back together either.