Flexibility is a very important and often a "hash-hash" component. It's not something you will see in a Rocky movie or in a public exhibition training session by a world champion boxer. It's something that happens behind the scenes.
Why is stretching important? There is a very long detailed answer to this question. We'll try a shorter approach.
ā€‹Core movement. Regardless if you are looking to rotate the core into the punch or flex to the side to avoid one; How far you can move without effort depends on your flexibility. Your opponent is used to fighting boxers of average flexibility. That means that he subconsciously expects your moves to start somewhere and end somewhere. If you can extend that range. You throw him off severely. Enough to make him nervous. At the same time you can reach further with your punches and get further away from his.
Leg movement. What applies to core also applies to the lower body. However because the power is generated from the ground, flexibility allows more of it to be produced. This has to do with most efficient ranges. The muscles are the strongest in the center of movement. Flexibility allows that center to be large, thus more time/distance to produce power. This power can be used to increase the force of the punch or move around the ring more effortlessly.
Boxers often used basic stretches taken from yoga. Most of those are relaxed stretches, which slow down and relax the body. Not favorable characteristics when going into a fight. Zaichik Stretching Techniques don't have that effect. They develop flexibility much faster, without slowing the muscles down. At the same time Zaichik Stretching Techniques avoid the pain of the stretch reflex.
ā€‹This program also include strength exercises to help retain the flexibility and use it correctly in the ring. Boxers using this program reported ease of movement and faster recovery after matches.