When does one make classes?

I’ve coded in AS 2.0 for about one and half years, and migrating to AS 3.0 has been very difficult specifically because I never really dabbled in creating my own classes as my projects have very limited scopes.

I understand that classes are great for reusability, encapsulation, and modularity. In spite of that, I’m still finding it hard to figure out when is a good scenario to use it.