As Dave M said -- depends on what you are hauling! My main criteria is to ensure that that the momentum of that object does not bring it forward on the trailer and into me and the truck. If that is an 800 lb small Kubota (on a 14ft trailer with strong perimeter rails going 12 miles away) a couple of straps is sufficient. If it is the 9,000 lb MF 2660 with 1000 lb bucket on the loader and a 1460 lb 7ft bush hog on it that takes the multiple 3/8" chains and not the 5/16" lighter ones. And of course proportional grades in between for less heavy loads.
I treat stopping forward motion in a potential collision as the #1 driver. Second is keeping the tires under significant force downward onto the trailer bed where brakes and gears help, and Third is prevention of other motion such as that caused by steep hills, rear end collisions, side hits, deep unforeseen potholes, etc.