Why do people make an actions layer in Actionscript? I thought we were supposed to use classes?

Some people use classes in games, and it seems to be more professional, but I'm trying to learn how to make my own, and really need to know if what I'm using for tutorials are crap or if they will help me in the long-run. I want to know the most professional, and easy collaborative way to program with Actionscript 3.0