Catalogs tell the librarian what's newly published. What information is currently available to their patrons. Librarians not only don't throw away catalogs, they circulate them to other librarians, file them for reference, and refer to them for up to three years after the catalog is mailed. Librarians are serious buyers. Nothing could be further than the truth.
Librarians are consumers just like everyone else.
One publisher I worked with had a lot of microfilm locked in their vault that had never sold one copy in 3 years. Within a year, this one catalog generated over a million dollars from the library market. Librarians won't buy a book that hasn't been reviewed. While reviews are extremely important for some libraries, the simple fact is that most books don't get reviewed because of the editorial policies of the review journals and the limited space of librarian-oriented magazines. Librarians do purchase un-reviewed books if they fill a gap in their collection.