One advantage is that if the modules are distributed to others then the amount that they need to type into the httpd.conf file is reduced. It also means that the module authors get control of the url layout and so can change it without ever changing the httpd.conf file - ie easy upgrades. For something like a drop in blog or mail solution this would be vital.

Another reason is that you can then ensure that the user has jumped through some hoops before letting them get as far as the next modules. This could be authenticating them or setting up variables based on their preferences.

Also the layout does not need to come from a hash, it could come from an XML file. This opens up the possibility of allowing plugins to be added to a site automatically - the plugin would register itself in the XML and the handler would then know that it could dispatch to it. There is more needed to make this work (ie modding templates etc) but it allows for it.

Finally it allows the _possibility_ of running the same code as a plain CGI (although the $r would have to be faked up). This would not be trivial but there would be one less obstacle.