With the tongue or pole a team always pulls toward the general front. The doubletree is directly behind them all the time. The tugs are putting little lateral pressure on their legs. The horses are relatively comfortable and their stamina is greater than if the traces were being pulled against their legs, as is the case when a pole is not used. The pull on their collars is more square or equal, as the tugs are kept fairly even by the doubletree.
Most teamsters are familiar with the pole that attaches to the implement and swivels up and down.
This style is, in my opinion, the easiest for the teamster to use and easiest on the team. If the pole is on a wagon or carriage that will be pulled at a trot, this configuration is especially desirable, for the pole will gently move up and down as the horses trot. Even with this type of pole you have to adjust the harness so the brichen is snug, but not tight. The pole on my work sled connects so low that it takes a good deal of adjusting to get it down where it belongs. Here is where my D-ring harness comes to the front, for it adjusts quickly and easily.