Why would you make a whole class sealed/final?
inheritance, oop, polymorphism
Solution
An organisation/software dev team might want to enforce certain coding standards. For example, in order to improve readability, they might only want attribute X of class Y to be modified with method Z and nothing else. If the class were not final, some developer might extend class Y and add method W, which could modify X in a different way and cause confusion and delay when it came to comprehending the code written.
Problem
I understand the motivation for making individual methods of a class `sealed`/`final`, but what purpose does completely prohibiting inheritance from the class serve? While allowing overriding of certain methods can cause bad things to happen, I can't see how allowing inheritance from your class purely to add behavior to it without overriding existing behavior could ever be a bad thing. If you really want to disallow overriding anything in your class, why not just make every method final but still allow inheritance for the purpose of adding behavior?