They could catalogue you. Librarians wield unfathomable power. With a flip of the wrist they can hide your dissertation behind piles of old Field and Stream magazines. They can find data for your term paper that you never knew existed. They may even point you toward new and appropriate subject headings.
People become librarians because they know too much.
Their knowledge extends beyond mere categories. They cannot be confined to disciplines. They bring order to chaos. They bring wisdom and culture to the masses. They preserve every aspect of human knowledge.