It's mostly useful when you migrate website and can't preserve your URL structure. Set up 301 redirects from your old pages to your new pages, any incoming links will be seemlessly passed along and their page rank will be passed along with them.
安装:
Upload Redirect 301 to the /wp-content/plugins/ directory.
Activate Redirect 301 plugin through the 'Plugins' menu in WordPress3. Add redirects on the Settings > Redirect 301 page.