Consider a few of the benefits not mentioned in the article:

- You have reduced the cyclomatic complexity of each class, which makes the code less fragile and easier to unit test.

- When adding a new operator, you are now forced to implement everything it needs to work. If you don't define a method, it won't compile. This is not the case with a long list of if/else statements.

- "You still need a nest of conditionals when you populate the tree..." This is true, but now all the conditionals are in one place, rather than two (in their example, toString and evaluate). Again, this will make testing easier.