Suppose, for example, that we have three buttons in three different movie clips, all with the same purpose. Instead of triplicating our code, we can put one copy in a function on the main timeline and invoke it from each button as needed. This saves time, reduces the potential for errors, and makes it easy to update the behavior of all three buttons at once. Because the code is centralized, testing is more reliable and troubleshooting much easier. If one button works and another doesn't, chances are that the problem is in the second button's function invocation and not in your centralized behavior.

9.11. Functions as Objects		9.13. The Multiple-Choice Quiz Revisited