Big chore days give us all a chance to work together, in a way that smaller normal chore days don't. The leaves in the fall is a great job for all ages to help out with, and this year I judged Carbon to be old enough and coordinated enough to climb the ladder and go up on the roof with me to sweep it off and clean out the gutters. As he's been flirting with a fear of heights, this was also a good chance for him to face some fears.
He ended up freaking me out, dancing on the peak of the house like the chimney sweeps in Mary Poppins. OK, not quite that bad, but he got really comfortable up there.
Besides getting the job at hand done, there are so many other benefits of this kind of family activity: demonstrating work ethic, teaching basic skills, open-ended family time that invites conversation, the sense of camaraderie that comes from a shared task, and time outdoors in the fresh air. I'm sure there are more that I'm not thinking of right now.
I would put family chore time right up there with family dinner as one of the most important glues that holds families together.