Choose an appropriate display object.
ActionScript 3.0 includes a large set of display objects. One of the most simple optimization tips to limit memory usage is to use the appropriate type of display object. For simple shapes that are not interactive, use Shape objects. For interactive objects that don't need a timeline, use Sprite objects. For animation that uses a timeline, use MovieClip objects. Always choose the most efficient type of object for your application.
The following code shows memory usage for different display objects:
trace(getSize(new Shape()));
// output: 236
trace(getSize(new Sprite()));
// output: 412
trace(getSize(new MovieClip()));
// output: 440
The getSize() method shows how many bytes an object consumes in memory. You
can see that using multiple MovieClip objects instead of simple Shape objects
can waste memory if the capabilities of a MovieClip object are not needed.