Differences between ABAP and OOABAP

OOABAP and Procedural coding can be mutually done in ABAP. Is is an advantage. We can include OO ABAP coding in the traditional procedural coding of ABAP. you will not have any issues. 

As OOABAP is a class based concepts, most of the OOPs advantages are inherited to OOABAP. Because Object oriented ABAP, the resultant advantage set include unifying data and functions, polymorphism, inheritance etc.

BadI is built on OOABAP as a class based concept because polymorphism and object orientation is of great advantage. However, traditionally this concept was based on customer exit and cannot be run for multiple methods hence BadI with OOABAP was developed.