I should not say 'yml based settings' is a deal-breaker but it sure is a very good way of configuring the project. I personally take advantage of this convenience quite often.
You can easily update your schema through yaml files and you can build&generate your whole model including auto-generated forms & filters for CRUD in a glimpse. I believe this is very friendly with agile principles.
Yes you are right. But It does not have to be all about yaml format itself. Instead, Symfony utilizes this format to get things done in a fast and neat way, in comparison to others.
