Purpose of final and sealed

Question

Why would anyone want to mark a class as final or sealed?

Answer 1

Because creating a type for inheritance is much harder work than most folks think. It is best to mark all types this way by default as this will prevent others from inheriting from a type that was never intended to be extended.

Whether or not a type should be extended is a decision of the developer who created it, not the developer who comes along later and wants to extend it.