Why does it need the use if its already a parameter?

It’s a dependency injection pattern. The decorator is telling some other piece of code what to pass in to that method, or to set some hidden context.

I’d check the docs for what it specifically does, but the site is completely unusable on iOS.

It would make more sense if the injected variable was an interface, the decorator telling you what the concencrete type should be. I think? Otherwise, yeah totally pointless.