Yes, why is it so important? It looks everybody around there (experienced and in-experienced) love its so much. You may wonder How could this methodology be more than to compose behavior and attribute of a real world thing into a class and use its along your application. If you just did it like that, the point is, you still didn’t use any object-oriented analysis and design!
It’s good to do the things like above, but that is just a first step. You need to do more, even though you already applied some interface implementation and abstract classes and those inheritance. The point is,
you already know about OOP’s definition and how-to do them, but may be, you didn’t know why and when to use them.
Whenever you know ‘when’ and ‘why’ to use those principle, you would see a big improvement in your existing system. Your design will transform to more (may be the most) flexible things, and finally, you will got a really “framework” which most flexible and also make your work (include your team) feel more happier when there is any change, or extend.
I will continue this next time, comment if you want 
