No one likes to work with the legacy projects - it's not fun. There are no specs, there are no behat examples and you're afraid to touch it. The customer may not have time or budget to spend on rewriting it from the scratch, but is likely to keep asking for the new features.
Learn how to work with the legacy code, how to add new features without breaking existing ones. Learn to use Symfony components to support building sustainable features.
What a Symfony developer should know about the framework: News, Jobs, Tweets, Events, Videos,...