There are many reasons why you might redirect an existing URL to another. Sometimes you just want to change the URL of an existing page. Other times you might be removing an outdated or duplicated page in favor of a better page. Regardless of the reason, you need to redirect the old page to the new one to ensure that the search engine knows what you are doing.
A permanent redirect, or 301 redirect, tells your search engine’s spider the permanent address of the new page and directs all traffic to that page. (It works to direct people using browser’s, too.) While you may need to work with your IT resources to configure the 301 redirect, it typically provides the most effective way of informing your search engine’s crawler of which page it should point searchers to.
By doing this, you ensure that the search engine does not keep trying to show searchers the old deleted page.