PHP frameworks provide basic functionality and an architecture for building projects. They promote code reuse and speed up development by reducing overhead code needed for tasks like database access, authentication, and validation. While frameworks have learning curves and performance costs, they make code easier to maintain. Popular PHP frameworks include Yii, CodeIgniter, Symfony, Laravel, and CakePHP, with each having their own strengths for different project needs and team sizes. Frameworks help developers build clean, reusable code by enforcing separation of logic and presentation using patterns like MVC.