A hitch that hard mounts to the front and back are the best method for towing. Once you start trying to tow from the 3ph, (as mentioned) it's reliability and safety factor (terrain and load based) can change in an instant. Example: 3ph is set very low. While towing on flat ground, "most times" all goes fine. Now same scenario, but with a hump, or rise in the travel path. All is fine until the rear of the tractor crests the rise and down the other side. As the trailer tongue begins to crest, the weight on the back of the tractor becomes less. Next thing that can happen is the 3ph and whatever you are towing, lifts the 3ph to its highest position. The situation (again, given the load) "could" drive the tongue of the trailer right through the seat and injure the driver.
It may sound far fetched, but I think outside the box of norm.