@nprofile1q... Apple will just shred it.. so it's "recycled" for the metal.. but they're not re-using it.
In my experience, it's best to wipe it, then set it up with a new local account with a dummy admin password.. then put it as a sticky note on the keyboard.
If you plan for it to be useful again. You don't need an icloud password, just a local admin password.
Hope that helps!