Search friendly urls will help your website to be properly indexed by search engines. It only works with Apache webserver so if you don't have this then leave it switched off, but if your are knowledgeable it is possible to make it work with other web servers.
The website uses the .htaccess file in the base dir which forces "index" in the url to be treated as "index.php", for example:
evil URL: ../index.php?type=article&menuID=6
friendly URL:../index/menuID_6-type_article