Why do I need to define an abstract class/method

Question

Why do I need to define an abstract class/method when the declaration in the subclass for the method would do the same thing it would do without the declared abstract method.

Answer 1

To allow pollymorphism, improving the maintainability of the codes/classes.

This is also situational. There is no "need" to always do one thing in programming.

Answer 2

That I can do without it then?