Yes if you are doing small size, concentrated boils then adding the extract late will prvent scorching and mailard reactions. As to how much this greatly depends on the equipment you use, the heat source (IE gas vs. electric) and your technique.
Im not sure Palmer mentions it, but my opinion on the technique is that it is best to add the late extract to the wort immediately when you turn the flame off....stir it in and keep it hot for a good 10 minutes before diluting with water. This will insure that any nasties the extract may contain are killed from being in contact with 180+ degree wort for a few minutes. Dilute with water afterwards.