The American College of Sports Medicine recommends that endurance and strength training athletes consume higher levels of daily protein than the standard recommended daily allowance (i.e. 1.2-1.7 grams of protein for each kilogram of body weight, versus 0.8 grams per kilogram per day).
It is basically a way (or excuse) to drink straight bourbon that tastes diluted, a much easier (and faster) to consume mixed drink, but is in fact near full strength.