Whenever possible, put your ActionScript® in a single location. Organizing your code in one place helps you edit projects more efficiently, because you can avoid searching in different places when you debug or modify the ActionScript. If you put code in a FLA file, put ActionScript on Frame 1 or Frame 2 in a layer called actions on the topmost layer in the Timeline. Alternatively, you might put all of your code in ActionScript files. Some Flash Professional applications do not always put all code in a single place (in particular, ActionScript 2.0-based applications that use screens or behaviors).
You can usually put all your code in the same location (on a frame, or in ActionScript files), with the following advantages: