There are a number of reasons why someone would need to use a 301 or permanent redirect.

1. The website may have been redesigned, and the new hierarchy does not match that of the old web site.
2. The website may have been restructured, which can happen as the content of a website grows and the link navigation needs a major update to improve the user experience.
3. The website may have been moved to a new host.
4. The domain name or URL may have been changed, but the old content kept.

Web Forwarding

A 301 redirect is also known as a permanent redirect. This tells the search engine that the content that used to be there has been permanently moved to a different location, and then tells the search engine where that location is. Most domain registrars make 301 redirects easy. They usually refer to the process as "forwarding" and ask you to supply the old URL and then the new URL where the web page now exists. When entering the forwarding URL, be sure to include the exact location, including any file names that may follow the URL.

Remember to 301 Redirect!

The web crawlers will probably find where you've moved your web page or website and index your changes. Where the pitfall lies is with people who may have book marked a particular page of your website or a cached version of your web page that is still being indexed by the search engine. Without a proper 301 redirect in place, a 404 page not found error could occur. This creates a bad user experience for someone trying to get to your website through a bookmark. If too many 404 errors are generated, the search engines may interpret this as your website no longer being available, and your entire website may be removed from the search engine index.