Sometimes the corks give the baits a completely different action. Wave action imparts a much different action than the line coming off of the rod tips. Corks can move ever so slightly with wave action, where as my pontoon takes a pretty good wave to move or bounce the rod tips.
I usually try a mix of cork rigs, and straight un-corked, until one seems to work better. Some days it doesn't matter, with both styles staying in for the day. Small corks, properly balanced, provide far less resistance for the fish to feel when taking the bait, than a rod tip. If they are hitting hard it becomes irrelevant. I think I just like watching a cork go under.
I also think that using a cork helps to set the hook on a light bite. Fish takes the bait, without feeling the resistance of the cork, moves the bait off a few feet, and then gets to the place where the slack is all out, and the rod takes care of the hookset.
"Hello, My name is Bill, and I'm a tackleholic"