awesome it would be if we did. But as my wife can attest to, weeding and I don't get along. And yet I do it professionally.
The answer, of course, is that it's library-speak for removing materials from a collection, and this is something that can be very upsetting for some people. But it's very necessary for a collection to thrive.
Look at it like this. When you weed a garden, you're killing some plants so that other plants can grow. If you have some tomato plants that are wilting and dying, you sometimes have to yank them out to make room so other plants can succeed. (Okay--I'm going to end the gardening analogy now. I'm out of my league when it comes to the proper care of plant things.)
In a healthy library, books will come and go. Ideally, all our books would be loved, cherished, read and used. But that's not the way it plays out. Some books get scribbled in (not by you, surely!). Some books get taken to the bathtub for some light reading before taking a quick dip. Some books get gnawed on by beagles. In these cases, these books will typically just get replaced, after we charge whoever allowed such atrocities to happen.
But what happens when a book just sits there, year after year, unchecked out? What do you do with those books? Sometimes, you hang on to them. Just because people aren't with it enough to realize a classic should be read and checked out doesn't mean you throw that classic out. On the other end of the spectrum are books that clearly have outlived their usefulness. Books like Do It Yourself Coffins for Pets and People and Don’t Make Me Go Back, Mommy: A Child’s Book about Satanic Ritual Abuse. (These books, by the way, come to my attention from the often funny Awful Library Books blog, a blog I recommend.)
The trick is that some people view all books as inherently worthwhile. To make matters more difficult, they tend to believe books are like fine wines--they increase in value as they age. So while one person will look at an 1830s map book and see value, another will see it's molding, wormy, water damaged, brittle, and it hasn't checked out since 1831. Do you keep it, or weed it?
What a library needs to do is identify its purpose and then stick to it. Shelf space is limited, after all. If the library is focused on collecting complete map collections, maybe that book can be saved. If it's trying to give the public access to relevant timely information, it's probably time for that book to go. We librarians have to make these decisions all the time. Some decisions are hard, some are easy, but each one has the potential to turn into a public relations firestorm for the library. However, if we don't do it, the collection becomes difficult to use, irrelevant and eventually dies.
Just like a garden.
Or so I've been told. :-)