Question: Why would you use Google Book Search?
Answer: Google Book Search (unlike Diamond or WorldCAT) searches the full-text of the books in its inventory. Diamond and WorldCAT are limited to searching only title, author, subject heading and other specific and limited information about a book.
Because Google Book Search lets you search within books, you can see a table of contents or an index or just a portion of a book. You can then locate the book in a nearby library.