Has there been a case in practice where an object needed to be made immutable?

Yes, there was a case in real practice where an object needed to be made immutable to ensure thread safety and prevent unintentional state changes.

For example, in a multithreaded environment, the application configuration object was created once and passed by reference to different components. To avoid synchronization issues and data races, the object was made immutable — all fields were final, and modifications created a new object.

This increases reliability and simplifies debugging, as the object's state does not change after creation.