I believe the safety chains are to prevent the towed object from going in to the other lanes and hitting someone. I have had a 14' tandem axle trailer come loose at 65mph and it was a wild scary ride. Trailer was banging in to the back of the truck, weaving back and forth to the limits of the chains and finally broke free, crossed in to the on-coming lane almost taking out a car, then went down an embankment and 30 yards in to the swamp. Whew! Took a couple hours to fish it out and hook it back up properly.
I had forgotten to switch out the 1-7/8" ball for the 2-5/16.
Could have turned out badly for me and the other car.