I can see two options are Action script File and Action Script Class in File -> New from menu.
What is different between Action Script File and Action Script Class whether both are identically same or not?
Most of scenario i used Action Script Class only so i would like to know when we have to go for Action Script File?
Action script File and Action Script Class as both *.AS files.
The only difference is that the Class will generate all the package/class/constructor code for you while a File - won't.
If you wander why is an AS file is needed:
In short - there's no particular reason