It is difficult for me to explain as English is not my mother language. You must know what is drooping electrical characteristic of SMAW and TIG machines, it is related to U-I chart.
Unlike SMAW and TIG, MIG/MAG has almost flat characteristic. The lenght of arc at MIG/MAG is defined with voltage settings, you cannot reduce it or increase it. It is constant all the time. Therefore MIG/MAG machines are called CV machines (constant voltage).
SMAW and TIG are so called CC machines (constant current, constant amperage), and while welding when you vary the length of arc and so you change the voltage, but the amperage is almost the same no matter if you work with short arc or long arc.
At machines without arc force, if you reduce the arc almost to zero, the voltage drops close to 20V and the amperage is the same as well as you worked with normal arc length. But those heat input is small and cannot penetrate or melt the base metal and with a bit of pushing the electrode, you stick it to the metal.
At machines with arc force, when you reduce arc length, and voltage drops bellow some value, there is sudden and big increase of amperage that is enough to melt through the root.
Arc force is very helpful with cellulosic and basic electrodes.
Let me make an example. If you work with SMAW machine without arc force with electrode 3.2 mm, and you set 120 A, when you reduce arc length, the real amperage will be around 120A all the time until you stick the electrode to the metal. If you do the same with arc-force machine, when the arc lenght and voltage become lower than some value, the amperage increase to 180 A. This is used often when you weld roots, so often push the electrode in the root to make "key-hole" or "pear-hole". But, without arc force, instead to make key-hole you stick electrode, and with arc force and great increase of amperage you "destroy" the land of the root and make a key-hole in the gap.
I would be glad if you understand what I wrote