CQ5 or AEM has a handy configuration which can be used to reduce the size of client side file (like css/js) and can help in reducing page load time for CQ application. The configuration uses YUI compressor to minify the client side file sizes. YUI is utility provided by Yahoo. This reduces the time as you don’t have to manually go and use the YUI classes because CQ minfies the file size on its own.
Additionally, this configuration also allows you to debug client side files individually. We all know that by using client libs of CQ all the js and css files are rendered combined. However, if you want to debug them individually there is a way out for this as well, just check the debug checkbox and you will start seeing the files being rendered individually.
The utility can be checked here find the service (Day CQ HTML Library Manager). Click on the snapshot below to get more idea.