Let's say you have changed the location of one page to another. Since the url for the page has changed, when some other tries to reach that page via Search Engine or a Bookmark, they would get a HTTP 404 (Page not found). This is not good use experience and would eventually result in traffic loss. In order to prevent this, we can setup a redirect at the Web Server level to seamless go to the new url when some one clicks the old url in their browser.