Does a pre-rub coating really do anything?
I have seen and heard of many schemes for a pre rub coating on meat. Some use mustard, claiming it makes a better bark. Some use oil, claiming the oil-soluble spices in the rub penetrate the meat better.
I have used rubs with and without a coating and never found it to make a lick of difference in bark quality or flavor. Just about the only thing I have seen a coating matter on is the skin on poultry - a little olive oil seems to make the skin darken up a bit quicker.
So, does a coating really do anything? Is there something more subtle in the flavor difference than I am picking up on? Is it just something that allows one cook to say they do something different than another? Is there any consensus?
What say you?