One of the worst things people do to their site, and what can really bug SEO specialists, is to move pages around. Some websites, unaware of the harm they are causing may decide to change file names, move pages to different files or even change a domain name. This causes the following problems;

• You break all the incoming links that were pointing at that page.
• You break your user's bookmarks.
• You give the search engines a Not Found error, causing them to drop your page from their listings.
 
In order to prevent these errors you need to put a redirect on the original URL to the new URL so that all of your existing users and search engines are sent to the correct place and therefore avoiding the Page Not Found errors. When you are optimising a website you are trying to increase page rankings, if the search engine cannot find the pages then it is as good as dropping your page off the face of the Earth.

The 301 Redirect is a status code that will show when a visitor (human or SE) goes to one of your webpages that no longer exists, this particular status code tells the visitor that the page has been permanently moved to a new location. It also tells the visitor the new location of that webpage, so that search engine spiders can then update their records for that page. This means that the page will stay in the search engine's index and that PageRank and incoming links for that page should be transferred to that new location. Without the 301 redirect, the search engine receives a 404 Not Found error and the page is dropped from the search engine's index. All PageRank and incoming link equity for that page also disappears.

Some webmasters use the 302 temporary redirect to move pages which will not help anyone, besides going against the specifications of all the major search engines, the 302 redirect is extremely unreliable - no one (including many search engines) know how a search engine is going to interpret it, and the consequences are often negative.