Added a note about the advantages/drawbacks of listeners/subscribers

Author: javiereguiluz

cookbook/event_dispatcher/event_listener.rst

@@ -238,3 +238,16 @@ done as follow::
     Two types of request are available in the :class:`Symfony\\Component\\HttpKernel\\HttpKernelInterface`
     interface: ``HttpKernelInterface::MASTER_REQUEST`` and
     ``HttpKernelInterface::SUB_REQUEST``.
+
+Events or Subscribers
+---------------------
+
+Listeners and subscribers can be used in the same application indistinctly. The
+decision to use either of them is usually a matter of personal taste. However,
+there are some minor advantages for each of them:
+
+* **Subscribers are easier to reuse** because the knowledge of the events is kept
+  in the class rather than in the service definition. This is the reason why
+  Symfony uses subscribers internally;
+* **Listeners are more flexible** because bundles can enable or disable each of
+  them conditionally depending on some configuration value.