What are the advantages of a 301 permanent redirect?

The 301 server code is the only code that allows you to inform the page requester that the file he tries to access had been moved permanently. It can be very useful for both navigational and SEO purposes.

The advantages of 301 redirect for your visitors.
By setting up a 301 redirect on the pages you permanently moved, you can easily give your visitors the better user-experience of your website. With a 301 redirect, you can be certain that your visitors will not access an obsolete version of your site, but will find all the last pieces of information they need on your pages.

The advantages of 301 redirect for Search Engine Optimisation.
301 redirects are above all important from the point of view of Search Engine Optimisation (SEO). As it is the only server code that indicates the permanent move of a page to a new address, it is also the only code that is completely understood by search engines when indexing a site. Using a good server configuration, and well designed 301 redirects when releasing a new version of your website is thus crucial for your presence on search engines, and your potential incoming traffic.