The LCSH is a Thesaurus
Find new words for your topic
Sometimes no matter what you try, you can't find enough about your topic in the library catalog. Sometimes you get a word stuck in your head and you can't think of other words to try. It's times like these when the LCSH is a great brainstorming tool. Look through a copy and explore the vocabulary related to your topic.
Use the LCSH to pick up new terms for your topic, to get ideas for broader terms (useful if you can't find enough on your topic) and to find narrower terms (if you need to focus a topic).
When you find words in the LCSH books, you can search the words in the library catalog using either the subject or keyword search.