I use tubing and totally free running lead. The reasoning behind the tubing for me is that when we hook a fish it sets off in the opposite direction to our strike or tension, thus the line is scraping down the fishes body. Some protection is given to the fish by having a short hooklength plus lead then tubing . My fishing friend has a set up which has a breakaway lead on impact so only a short length of line comes into contact with the fish on impact the rest is a length of tubing which can roll across the body of the fish so causing as little damage as possible. He has the best method from the breakaway point of view but if we hit a runs water he can drop off £35+ of leads in a 24 hr session.
Nicks view that it is a distraction "across the dinner plate" I cannot see, as it is a swivel and hooklength away from the dinner plate and I cannot see carp as being that discerning as to leave the table because they do not like the look of a piece of something alongside it and probably a foot away.
I think we can over elaborate at times and give fish more credit than they are entitled to.
If I can protect the fish and prevent harm coming to them and it results in less fish coming to my net as a result then I for one am prepared to do so. I would love to do it my mates way and set my leads to break off on strike but at £35 per session plus the cost of the session, bait, petrol etc
we have to work within our budgets.