I have made several PHP loaders for YUI over the years, and it's nice to see this library come about. Taking a look at the examples, I can see that I had the right idea. The PHP Loader is more robust and cleaner than my implementations however.
So, the problem this PHP code solves is loading your scripts or YUI scripts dynamically on page load without having to write any of the YUI loader script.
In the YUI PHP Loader, they have somewhat simplified the insert() calls in providing $loader->css() and $loader->script() methods to print the script I have above.
Something that the PHP Loader does that I have not added to my own modules is the combination handler. This is where the backend gathers up all the scripts that you want, and combines them into a single download. This dramtically improves page load performance, and saves bandwidth.
Other advantages to this is that the files are server locally, so your site does not have to rely on a 3rd party domain to serve the files. This is especially usefuly where SSL is required or where you can not use a remote server. This includes combining your own files along side YUI modules. To add your own modules, simply add them to the configuration files in lib/meta
You can also change the default skin in the configs. This comes in handy when your testing things and want to setup an override.
I really have been waiting for something like this, and I am glad it has come into being.