Board Thread:Theories and Speculation/@comment-3568954-20150530220024/@comment-25549954-20150530220926

You do know that shadow clone is a forbidden technique because it divides the chakra evenly among the clones clone, of course the time for training is shortened, it is more suitable for people with abundant chakra reserves, Kakashi explained that only Naruto could do training with this method because he has enormous chakra due to the tailed beast. If a normal shinobi makes a thousand Shadow clone that person would die because the amount of chakra to sustain life is consumed in creating shadow clones.