Jens Struwe has taken the time to write up a good summary on why we need a collection framework for ActionScript.

Unlike scripting for server environments, where we usually synchronously access the underlying data base and process those data more or less consecutively in response to preceding HTTP calls, in client applications we need to more seriously take care about how we manage storage and retrieval that data during the entire application lifecycle.

It’s good stuff and paints a pretty clear picture. Also, if you haven’t done so already you really should check out the mother lode: Java Collection Framework.