I have been studying JavaEE8 and practicing with some projects, understanding the new technologies like Servlet 4.0 and JSF 2.3. I have read in many forums and pages, in some I see that they say that `web.xml` and `faces-config.xml` are not necessary, because annotations are now used, but in some others they continue to use them.

In which cases should you continue to use the Web Deployment Descriptor-> `web.xml` and the application configuration resource file-> `faces-config.xml`?