Ok, you're right. Thanks for your explanations.
However, I work on a small project built on top of the Symfony console component. I thought I could put all my configuration parameters in one yml file, exactly like Behat does http://docs.behat.org/guides/7.config.html. Behat is using nested parameters and it's common to create a behat.yml.dist file to share within the project. For me this is both configuration and parameters. Am I wrong?