Learnt Symfony2 a while.
You just don't have to re-invent the wheel when you want to do a complex website.
If you want to collaborate with people, you already have an architecture (MVC) plus a nice template system very usefull in order to separate front-end from back-end (TWIG is cool).
Finally, bundles. Quality code often reviewed and checked by countless amount of people which does maybe anything you want.
So, if you want to do small things, vanilla PHP is enough. Maybe with PDO.
If you want to make some real website, frameworks are cool.