Builder pattern vs. config object

Question

The builder pattern is popular to create immutable objects, but there is some programming overhead to create a builder. So I wonder why not simply using a config object.

Answer 1

The builder pattern improves decoupling - your Product can be an interface and the only class that knows about the implementation (or implementations, in some cases) is the builder. If the builder also implements an interface then you can inject this into your code to increase decoupling further.

This decoupling means your code is more maintainable and easier to test.