Tried to write the important points more explicitly

Author: wouterj

reference/forms/types/options/data.rst.inc

@@ -3,22 +3,19 @@ data
 
 **type**: ``mixed`` **default**: Defaults to field of the underlying structure.
 
-When you attach a form type to a form, it becomes a field that initially maps
-the value of the corresponding property or key of the form's domain data. If
-you want to override the initial value which will be rendered in the view for
-the form or any nested field, you can set it in the data option::
+When you create a form, each field initially displays the value of the
+corresponding property of the form's domain data (e.g. if you bind an object to
+the form). If you want to override this initial value for the form or
+an individual field, you can set it in the data option::
+
 
     $builder->add('token', 'hidden', array(
         'data' => 'abcdef',
     ));
 
-    // Is the same as
-    $resolver->setDefault('data' => array('token' => 'abcdef'));
-
-.. note::
+.. caution::
 
-    The default values for form fields are taken directly from the underlying
-    data structure matching the field's name with a property of an object or a
-    key of an array. The ``data`` option overrides this default value.
-    It means that when the data passed to the form is an object you want to
-    edit, the `data` option will also override the value already set.
+    The ``data`` option *always* overrides the value taken from the domain data
+    (object) when rendering. This means the object value is also overriden when
+    the form edits an already persisted object, causing it to loose it's
+    persisted value when the form is submitted.

reference/forms/types/options/empty_data.rst.inc

@@ -9,20 +9,23 @@ empty_data
 
 DEFAULT_PLACEHOLDER
 
-This option determines what value the field will return when the submitted
+This option determines what value the field will *return* when the submitted
 value is empty (or missing). It does not set an initial value if none is
-provided when the form is rendered in a view (see ``data`` or ``placeholder``
-options).
+provided when the form is rendered in a view.
 
-It helps you handling form submission and you can customize this to your needs.
-For example, if you want the ``name`` field to be explicitly set to ``John Doe``
+This means it helps you handling form submission with blank fields. For
+example, if you want the ``name`` field to be explicitly set to ``John Doe``
 when no value is selected, you can do it like this::
 
     $builder->add('name', null, array(
-        'required'    => false,
-        'empty_data'  => 'John Doe',
+        'required'   => false,
+        'empty_data' => 'John Doe',
     ));
 
+This will still render an empty text box, but upon submission the ``John Doe``
+value will be set. Use the ``data`` or ``placeholder`` options to show this
+initial value in the rendered form.
+
 If a form is compound, you can set ``empty_data`` as an array with field names
 as keys and submitted values as string values (or arrays if nested fields are
 also compound).
@@ -34,6 +37,7 @@ also compound).
 
 .. caution::
 
-    When using `empty_data` as an empty string, the form will always return
-    ``null``. If you need to get an empty string to be returned, you should
-    use a data transformer, see the :doc:`/form/data_transformers` article.
+    :doc:`Form data transformers </form/data_transformers>` will still be
+    applied to the ``empty_data`` value. This means that an empty string will
+    be casted to ``null``. Use a custom data transformer if you explicitly want
+    to return the empty string.