A trailer with a running lead could still leave a fish attached to a long trailer, yes it might be minus the lead but the rig is directly tied to the mainline via a swivel, with the hit n run lead clip if you got the same trailer, the rig would come loose as the swivel is free of the mainline,and therefore you will only ever leave the rig attached once the line parts as the fish can move up the mainline and be free of the trailer. It is also a running rig but neater and IMO safer.