Redirection is a WordPress plugin which gives the user a very handy interface for easily creating redirection rules and keeping track of 404 errors – Page not Found – without requiring advanced knowledge.
The reason it’s important is because if a Search Engine has found a page, image or other item on your website and the location changes and the Search Engine isn’t redirected to a new location then it simply deletes that entry from it’s records.
If a person has bookmarked a URL on your website, or if someone created a link to a location on your site, and you change the location, then that link breaks and people trying to find your site no longer can.