Uses of readObject/writeObject in Serialization

Question

I was going through this article to understand more about Java Serialization process. When it comes to uses of readObject/writeObject I could see two use cases:

Answer 1

There could be several reasons for using custom serialization:

1. Performance.
2. Interfacing with external systems. (Beyond-your-reach or even simply non-Java systems.)
3. Needing a human-readable format.
4. Support for older versions of serialized classes.

To name just a few, but I'm sure there are many more.