If you read Nutrient Timing, you'll see that multiple university tests(read: unbiased and with no vested interest in supp sales) shows that high GI carbs immediately post workout replenish glycogen stores more efficiently, and when combined in a 3:1 or 4:1 ratio of the carbs to protein, enzymes responsible for fat oxidation were much higher. And we're not advocating high GI carbs consumed all day long- just immediately post workout in the said 3:1 ratio, and then in a 5 or 6:1 ratio the other way(protein to carbs) another 2 hours or so later.
The studies implementing a system like this(using maltodextrin and glucose), along with BCAA's(especially Leucine, as you mentioned), showed improvements in bodyweight composition, strength, and endurance, as well as being less succeptible to colds than control groups.