The FormExtension provides a service for building form in your application with the Symfony Form component. When the CSRF Service Provider is registered, the FormExtension uses the CSRF Protection avoiding Cross-site request forgery, a method by which a malicious user attempts to make your legitimate users unknowingly submit data that they don't intend to submit.
You can find more details about CSRF Protection and CSRF token in the Symfony Book.
In some cases (for example, when embedding a form in an html email) you might
want not to use this protection. The easiest way to avoid this is to
understand that it is possible to give specific options to your form builder
$form = $app['form.factory']->createBuilder('form', null, array('csrf_protection' => false));
That's it, your form could be submitted from everywhere without CSRF Protection.