Yes, they learn a lot of stuff they won't need for the actual job they will perform. If they switch jobs, they probably won't need it either, unless it's a very related job. For instance, if they become a painter, they learn all kinds of painting techniques that they will never apply. That's all fine and dandy, except if they just want to work painting houses, why they have to spend three years as an apprentice?
> But at the Berufsschule you still learn all the other stuff, for an example how to wire electrical Garage doors. If you later decide to switch Jobs, you'll be prepared.
If you already knew the one thing, chances are you could've quickly learned the other thing as well. Otherwise: https://en.wikipedia.org/wiki/You_aren%27t_gonna_need_it