Through creative use of mod_rewrite, several sites can share a DocumentRoot and yet still appear to be independent sites
Let's assume that you are running a site called www.fruit.yum, and would like to serve information about apples and oranges. You've already had much success with http://www.fruit.yum/apples and http://www.fruit.yum/oranges, but you are suddenly able to obtain the much coveted apple.yum and orange.yum domain names. You'd like to keep the existing www.fruit.yum directory structure for users who browse to directories under your new domain names (for example, to http://www.apple.yum/order or http://www.orange.yum/faq), but would like to deliver a custom page to users who simply browse to the front page (e.g., http://www.apple.yum/).
This is no problem with mod_rewrite. Let's assume that you already have a VirtualHost entry for www.fruit.yum like this:
<VirtualHost *> ServerName www.fruit.yum ServerAdmin firstname.lastname@example.org DocumentRoot /home/www/htdocs CustomLog /home/www/logs/access_log ...