As applications grow in size and complexity, the number of objects you use increases rapidly. Instantiation can be expensive. Even with the new GC advice API in Flash Player 11 and AIR 3, garbage collection can slow down or pause your application. One technique you can use to improve performance by decreasing the number of objects in your application and reducing how often garbage collection runs is object pooling. With object pooling, you create objects during the initialization of your application, store them in a pool, and keep reusing them.
Look at an example of object pooling in Optimizing Performance for the Flash Platform. You can also read about garbage collection and the new GC advice API in Garbage collection internals for Flash Player and Adobe AIR.