I'm not quite so organised, but I do have a similar method to cleaning up. I have piles instead of boxes though. I go through my mess and put it into one of three piles. There's a "keep" pile, a "throw out" pile and a "maybe" pile. Then I throw out the junk pile, have a small break (like getting a drink or something) and start on the "maybe" pile. I find that I have a lot more clarity about something the second time I look at it, and I can confidently keep it or throw it out with no regrets. Then I either sort the keep pile, or push it back somewhere, where it's still a mess but is a smaller one.