Board Thread:Theories and Speculation/@comment-43776375-20190915194614/@comment-4912646-20190916003628

I've always wondered about this too. I'm pretty sure Fukasaku explaining how the senjutsu chakra goes back to Naruto is the only time in the series we're told that chakra goes back to the creator (previously we're only told that experiences go back), but the way it's written, it's almost like we're already supposed to know that it's a thing. I figure actually creating the clone might use up some amount of chakra aside from what gets shared, and like Squinty said there's also the issue of people like Naruto wasting a lot of extra chakra when using a jutsu.

It's also possible that shadow clones are only considered dangerous because most people have too little chakra to begin with. So when they divide their chakra two or three ways, they become too weak to fight effectively, and when they divide it more than that they risk dying from lack of chakra. A careless person might split themselves into three clones that each use up a lot of their total chakra without realizing it, then even when the technique is ended and the remaining chakra goes back, the original will be left severely weakened. This explanation works even if creating shadow clones spends literally zero chakra.