The different between returning an object and response return?

Assume I have two actions methods action1 and action2:

Action1:

    public JavaScriptSerializer action1() 
    {
        var student = new Student() { First = "john", Last = "doe" };
        JavaScriptSerializer jsonStudent = new JavaScriptSerializer();
        jsonStudent.Serialize(student);

        return jsonStudent;

    }

Action2:

   public void action2()
    {
        var student = new Student() { First = "john", Last = "doe" };
        JavaScriptSerializer jsonStudent = new JavaScriptSerializer();
        jsonStudent.Serialize(student);

        Response.Write(jsonStudent);
    }

Assume my view has a Ajax call like this:

 <script>
     $(function () {

         $.ajax({
             url: 'AjaxCallsTest/action1',
             dataType: 'json',
             success: function (response) {
               //code here
             },
             error: function (response, status, xhr) {
        //code here
             }


         })
     })
 </script>

In the two cases one was written to Response object and the other has a return statement. my question even when there is a return, does it actually adds the jsonStudent object to the Response object if so writing action methods with return statements are meaningless?

Thanks.