Nowadays developing web applications usually requires a flexible process due to changing business logic, shifting priorities or new insights. Besides choosing the right methodology this also requires designing the application in such a way that this flexibility can be achieved.
Domain Driven Design fits this process as it isolates business logic in the Domain layer and separates it from infrastructure and presentation layers. Questions like where or how to store data or what to build (website, mobile app, API) can be addressed separately.
Doctrine 2 provides PHP developers with a powerful tool to create a Domain layer that contains business logic that is easy to unit test and therefore easy to expand upon in iterations.