Many people don't know how to throw fast punches that have force on them, though. And that's the problem. If you want to see a guy with two different jabs, check this out:
Finito Lopez applies two different types of jabs here in what a friend of mine described as a "pet, pet, slap" manner. The first type of jab has nothing on it, just a tapping applied from the shoulder, with the elbow still connected to the left iliac area of the hip. Thus, always threatening some force despite it not being there. Basically petting his opponent into docility. Then, every now and again he drops some weight on that left foot and shoots the jab upward with the "slap." Taking advantage of the initiative given to him by the opponent complying with being petted into docility.
The hard jab moves faster than the soft jab at least half the time. And his body jab also moves faster. This is because Finito was very well-schooled, and knew how to push subtly off of the back foot. He did have a problem of throwing his right hand from the front foot, and that's what got him floored against Rosendo "Bufalo" Alvarez, who threw his own right hand with the same speed and velocity that Finito throws his harder jabs with.