The text is taken from my blog where the preloader class was originally published.

Large, sophisticated applications need to be preloaded as much as asset heavy animations and games. However, large applications must manage a large number of assets and need to be built cleverly, so that changing one aspect of the application does not require that other aspects have to be rebuilt.

Most of the preloaders that I have seen on the web are for small applications, in which one tiny swf is used to trigger loading of one massive swf and report on the load’s progress. This is not appropriate for large applications, because they require multiple assets to be loaded, and the load-list to be manageable without asset swfs like the preloader to be republished.

The preloader class presents a strategy for preloading by creating a ~25k preloader which loads a configuration XML file that defines both a preloader animation asset and a list of assets to be preloaded. It piggy-backs the Bulk Loader library to provide bulk loading functionality, which is where the majority of the 25k of the resultant swf comes. More detailed documentation is contained within the source code.

Clearly a 25k overhead before an animation is loaded would be smirked at by many ActionScript coders, but here I am interested in a strategy for reusability, flexibility and scalability to which those who seek to squeeze a preloader into 10k or less cannot hope to aspire. The two preloaders seek to satisfy different demands.