Symfony fixtures allow you to populate the database with test data or initial data for development. By using the DoctrineFixturesBundle, you can define fixture classes that contain predefined data records. These fixtures are useful for simulating a real environment during development, testing features, or preparing demonstrations. Once defined, they can be loaded into the database using simple commands, resetting the data to a specific state. This makes the development process more efficient and consistent, ensuring that the application functions correctly with realistic data.