Studies have shown that the artificial sweeteners can actually cause you to crave sugar.
Simple answer: It doesn't. Only if you believe that you are not taking in calories you would have consumed drinkiing an ordinary beverage. Like everyone else, I ocasionally drink a "zero calorie" beverage, however the artificial sweeteners used in these drinks all are slightly toxic and some believe these substances can cause neurological damage in large doses. Moderation is the message.