Symfony is an Open Source distributed PHP framework. Of course,
when you know how to develop in PHP, you don't need a framework.
However, it is very nice to have one!
A framework helps you work better (structuring developments) and
faster (reusing generic modules). A framework facilitates
long-term maintenance and scalability by complying with standard
development rules. Compliance with development standards also
simplifies integrating and interfacing the application with the
rest of the information system.
Symfony is an internationally recognized, stable development
environment. An innovative and easy-to-use work environment thanks
to integrating solutions created in other environments such as
dependency injection (taken from Java) and specifically developed
solutions such as the Web Debug Toolbar or the Web Profiler.
Finally, by adopting *de facto* standards, Symfony does not confine
you to its environment, but allows you to choose the software
components that you want to use.