
In the United States, most public libraries have favored using DDC. The academic libraries have favored LCC. US Government publications are cataloged using SUDOCs. Medical libraries may utilize the National Library of Medicine classification schedule along with the specialized language of MESH.
There has been tremendous thought and energy put into the systematic classification and organization of library materials. With good organization, people not only can find what they are looking for, but they can also make connections to other ideas. The more you know, the more you know that you do not know.
If you consider the size of a traditional library catalog relative to the physical collection that it represents, it is miniscule. The language of cataloging has had to be extremely precise in order to maximize the relationship of a few words on a card of paper, to the physical work they describe. In order for every point of reference for every word and image in every document to be represented in a physical library catalog, the proportions would have to be reversed. It would be not be economically feasible.
The information age has changed everything. Now, every word of every document can be represented through full-text indexing and every part of a document can be searched. The new library catalogs have adopted machine readable cataloging rules (MARC) and the nature of searching has changed. You do not have to sort through paper cards pointing the way in a local collection. You can search thousands of libraries at one time from any computer with an internet connection and achieve instantaneous results.