This is an old post that explains how flex states work, how creating a state creates a Factory that holds a hard reference to the state, and a workaround for states if you want to be able to release the memory of a state.

Since this post, I've learned a few things, and before reading, I want to make a few corrections.

The garbage collection in Flash is all done behind the scenes, and it takes some tricks up the sleeve in order to ensure things get garbage collected, and also to check whether things are garbage collected.

This article has simple techniques as well as advanced. Read or skim what best suits you.

The first thing I want to write about is how to decide when and where to optimize something. I've observed that some people care absolutely nothing about optimization as long as the program works, and some people waste altogether way too much time optimizing things that make little to no impact.