Say you have the coolest MovieClip ever, say for instance
an enemy in an awesome Platformer game you're making.
It's completely perfect, coding and everything is done. It's great.
But now you need 9 more of them for that level.
And the next you're going to need 20 more, and
it just gets even worse from there. What do you do?
You can make your Enemy MC into a class.
This isn't as useful I think in AS2 because of duplicateMovieClip,
which doesn't exist in AS3. In AS3 you have to
make it into a class, and instantiate them separately.
Which is more organized, I feel.
As for an example, just use the link
the man above kindly mentioned.