Born, like other comic book characters, out of an otherwise trivial but life-changing animal bite, the Rabid Librarian seeks out strange, useless facts, raves about real and perceived injustices, and seeks to meet her greatest challenge of all--her own life.
But they are, and they can be used to fix nitrogen in the soil and also keep the soil from eroding. Here's a nice film from the BBC that not only explains that, but mostly shows lovely meadows of various wildflowers that I found relaxing.