The biggest benefits of proper inheritance are : a.) substitutability and b.) extensibility.
Substitutability – The objects of a properly derived class can be easily and safely substituted for an object of its base class.
Extensibility – The properly derived class can be freely and safely used in place of its base class even if the properly derived class is created a lot later than defining the user code. Extending the functionalities of a system is much easier when you add a properly derived class containing enhanced functionalities.