"One easily fixed problem that many websites have is
duplicate results in search engines. In any given search engine,
http://www.example.com/ and http://example.com are two completely
different websites. This is a big problem because the content in
your website is identified as duplicate content, and that brings
your search engine rankings down. Using our new friend,
mod_rewrite, we can assess this issue.
"At the top of any .htaccess file, you need to turn Mod Rewrite
on. This should always be at the top of your .htaccess file. You
only need to turn Mod Rewrite on once."