Christian giving really stupid advice, while Stephanie's trying to give nuance within a character limit.
So, here's how I view fandubs now, if you're looking to practice syncing voice to lip flaps, I don't see harm, but I'd keep whatever you did far away from your professional face.
Mike Varker
"Why aren't there any Anime fandubs on YouTube anymore?"
Because it hinders your chances of being in a real anime.
Yes, there is an explicit rule in this industry now not to do fandubs.