Most people on a regular "western world" style diet are already overeating, particularly when it comes to protein. Seen over the whole day, you won't need supplements until you're doing 2-3 hard and planned sessions daily. With that said, I believe I've noticed speedier recovery, hence better payoff from the next session, if I have a nutritionally sensible snack during the ideal time span right after a workout. And bars and shakes are easy to carry around. Makes me less hungry at meals too, so I don't think I've increased the total intake by much.