If the thermostat is right by the AC unit, some, like me, may prefer to have the sensor nearer to where we actually spend most time in the trailer. Additionally, if, like mine originally, the stat is an analogue device (e.g. a rotary knob with a printed range of temperatures), then it is not the most precise and useful controller.
A digital thermostat mounted on a wall in a more useful area solves these issues for me. The cable you describe may enable this modification with minimum wiring complexity.
I described full details of the fitting of my remote digital thermostat ,for the AC and the furnace combined, eleven years ago here: