Cataloguing: MARC 505 field

Why the cataloguers add the details contents of the items in the 505 field? The answer is simple. With the 505 field information, readers can have a quick information about the book when they look up the book via OPAC. And they will be able to determine whether it is the right book for their needs. As a librarian, I found the 505 field is very useful, especially for the technical and medical materials. Sometimes book title does not tell you what the book is about. The 505 field is a tool to know the book by first glance. Unfortunately some OCLC and Library of Congress records do not necessarily contain 505 field; thus library cataloguers have to add the 505 field after downloading the record.