This is because there is more efficiency and effectiveness letting each body part keep its optimal speed without slowing down to adjust to a heavier body part that takes more time to move.
That way you get maximum use of acceleration of each body part and synchronize it to maximum impact. Back in the 90's Imrich Lichtenfeld gathered his Civilian Black Belt recognizing it is essential to be able to have knock out power to end a fight. So out of prioritization he went over the basics.
If you notice that some of his old students who are black belts do not follow exactly his way of punching, you should ask yourself why. Perhaps the way Civilian Krav Maga organization was run...
While Imrich was still punching with his boxing habits, Eli Avikzer, his heir in the Israel Defense Force Fighting Fitness Academy had a different idea: teaching punching or strikes was more to concentrate on a quick efficient fast reach blow to the opponent without projection meaning without standing in a projected fighting stance.
Since Krav Maga defenses were built to counter an overall myriad of Human Capacity to deliver, kicks punches, blows and various strikes, or take down attempts, there was no use to many of the boxing drills, but rather to concentrate on effective and efficient strikes.
While Imrich is demonstrating what a punch should look like coming back to the center court after execution, as the IDF Third Krav Maga Chief Instructor I took it one step farther demonstrating by pausing immediately after the end of the punch (with complete retraction)that the next motion would be dictated with necessity, instead of automatically coming back to the center court.
I borrowed the idea as it was applied to other tactical considerations in Krav Maga and applied it to the drilling of punching in order to gain good work habits to be applied within an instance during a confrontation.
Instead of returning to the center court, you strategically evaluate what options your opponent might have next and follow up accordingly.
If you missed the first strike, and you are moving to the center court you are idling which subjects you to a counter attack...
This is a fighting tactic I've learned form Eli Avikzar, the Second Israeli Defense Forces Krav Maga Chief Instructor and I had put this tactical approach into the training steps of the hand Strikes learning process starting with the basic breakdown of the sequential execution training steps.
In addition it facilitates a better training breakdown to the correct sequential execution required for a KO Punch. It ensures your body weight is supporting the hand during contact and target penetration, which could be a few inches before or behind the estimated location when you start to lunge your strike.
In fast speeds the untrained eye would not notice the difference when someone is shadowboxing, but the idea is to slow down in training in order to assume control of the unseen.
I recall Listening to Imrich Lichtenfeld RIP, a well aged man in 1980 explaining the details of what a Knock Out punch should be sitting in a Cafe Ugati in Natanya, and occasionally getting up and demonstrating it...
Imrich Lichtenfeld a man that in his youth was a boxing champion, a wresting champion, a glamorous gymnast, but later in his life assumed the responsibility of training the Israeli to be Soldiers, and later the Israeli Soldiers in the working art of unarmed combat - Krav Maga!
Processing the information in my mind, and then in the next opportunity trying to check it myself and apply the advice... Thinking of any student anywhere looking at his instructor demonstrating in class a punch and repeating the motion with or without thinking the end result.
Better be thinking. How is this motion is going to stop my opponent... Listening to Instructors recommending breaking more boards or bricks, others recommend more workout on the punching bag....
Well Each training method develops some elements but not necessarily all that are required for a knock out strike.
Continuous attack the golden solution to control an opponent hoping that while attacking the the window of opportunity is increased for a knock out punch- only seems like a Good idea. But in reality, the window of opportunity closes immediately after the first attempt to strike. You need to know the whole theory before you attempt to use one idea of it.
The IDF training steps had to be modified for the favorite KO punch in order to simplify the complexity of any human motion and bring the soldiers for speedy control of the unarmed combat theory and application.
While many Martial Arts use the concept of timing, Pure Krav Maga chooses sequential execution under the constraint of reaction time. What is the difference then?
Well the results might appear the same but in fact they are not! When you see someone succeeding blocking on time or counter attacking on time during sparring, there is a victory! You call it timing. But how do you teach it? How do you teach it to each one of your students in the first few hours so their learning could be applied immediately if needed? Why leave it only for those that become long term disciples?
Well the secret of the recipe is trifold. First, realizing what is the fastest motion you can gain from the move you are intending to apply and what sequence of body parts motions to apply to maximize that speed.
Second, equally applying this approach to all methods of attacks and defenses so the result would be unchallenged. This is applying the Pure Krav Maga concept of Sequential Execution.
And last, knowing that the timing to commence the attempt to reach lies in an invisible area much farther than your body. It is about little less than fully extended arm. As a rule of thumb, if your arm is less than ninety degrees at the elbow if you are trying to block a straight punch, it probably would not work against an efficient attack. Markers are slightly different for kicks because the bio-mechanics of the body.
Watch Imrich Lichtenfeld Rehearsing Civilian Krav Maga Straight Punching Sequences and Boaz Aviram Teaching the Sequences through the IDF Intensive Training Steps!