That is one of the main reasons you use inheritance. You treat the SuperClass as an abstraction, and at compile time you don't need to know the derived type, or another class doesn't need to know the derived type. This allows you to use references to SuperClass while using polymorphism to call the methods of the derived class.
This enables you to
a.) Create factories so that you don't need to know the type at compile time, and you have some runtime method that creates the derived types. Think COM, GStreamer, DirectShow, Glib, etc...
b.) Hide complexity to other objects by only exposing the base type references even though they are instances of the derived type. Think about the methods that return object or take an object reference as an argument.
c.) many more possibilities, but those are probably the most relevant two uses to you.
