There are situations when you need not to index pages quickly, but to remove them from the search results. For example, when you buy a domain name, and create a completely new site on it, which is in no way related to the previous one. Or, the index contains pages that should not be there. Or you just decided to close a section on the site that is no longer relevant. article how to prevent google from indexing a page  will help you learn more about this topic.