dialog addField vs addFieldValue in Dynamics Ax

I think an example speaks by itself

class EF_DialogTrial2
{
    String20 myString;
}
public static void main(Args _args)
{
    EF_DialogTrial2 cl = new EF_DialogTrial2();
    cl.dialog();
}
protected void dialog()
{
    Dialog dialog;
    DialogField dialogField1, dialogField2;
    
    dialog = new Dialog();
    
    myString = 'ciao';
    
    //the difference between addFieldValue and addField is that in the first you can 
    //initialize the dialogue field with some value. 
    dialogField1 = dialog.addFieldValue(extendedTypeStr(String20), myString, 'my value');
    dialogField2 = dialog.addField(extendedTypeStr(String20), 'my value2');
        
    if (dialog.run())
    {
        myString = dialogField1.value();
        
        info(myString);
        info(dialogField2.value());
    }
}