My son is 9 and slightly ahead of the Lego curve. We have both a large number of freestyle Legos and sets of various sizes. When we open a new set, I always immediately empty all the pieces and sort by color.
With the last set my son opened, the 824-piece Volcano Exploration Base, he poured all the pieces onto a beige surface, one bag at a time, but we did not sort. Some pieces took him a while to find, but overall it took him about the same amount of time with about the same error rate as a set we sorted of equivalent size.
So, my question is, moving forward, as we wind up with larger and larger sets, will his method continue to be about the same efficacy, or will he just get overwhelmed?
What I don't know is if the larger sets also have numbered bags for various portions of the whole such that one could open a few hundred pieces from a single bag which then goes on to make a particular structure.