The push/pull/legs split is probably the most efficient workout split there is because all related muscle groups are trained together in the same workout.This means that you get the maximum overlap of movements within the same workout, and the muscle groups being trained get an overall benefit from this overlap.For example when you train chest with say bench press, you are also hitting your anterior deltoids and triceps hard. And when you train shoulders you are again involving your triceps. ~ Berceste