Wing-Chun values speed over power. However, having the power on top of the speed is a bonus. A fast punch that is too fast to be avoided is better than a powerful slow punch that can be dodged or deflected. And again, a powerful slow punch can really hurt.
Striking inevitably opens up part of your own body to be attacked. A fast strike reduces the exposure time. A punch is faster than a kick, so punches are emphasized over kicks. This does not mean that Wing-Chun has less kicks than punches (a well rounded Wing-Chun fighter should be able to blend all the kicking techniques into the punching techniques equally 50/50). Punches are also safer as they do not disrupt the body’s centre of gravity as much as kicks do. Wing-Chun kicks are kept low, below or slightly above the waist, so as to not to be grabbed by your opponent’s faster hands (again, this is consistent with the Six Points Harmony theory). A Wing-Chun practitioner who is committed to the system would gradually learn how to utilize kicks as often as punches.
Wing-Chun’s emphasis on speed arises naturally from its close range fighting focus. At close range, a punch has less distance to travel and so will meet the target more quickly. At close range, hand positions can be difficult to see because of this heightened speed and Chi-Sao comes in handy because it helps the practitioner to rely on sticking with the opponent’s limbs without watching. This is the main purpose why Chi-Sao is used to train a Wing-Chun practitioner to sense his opponent’s hand position and probe for holes in his defense, from touch alone.
The Wing-Chun stances are also designed for speed. The feet are kept about a shoulder’s width apart, forming a good balance between speed and stability. A wider stance would be more stable but would slow down kicks and footwork.
A highly trained Wing-Chun practitioner achieves maximum speed by acting reflexively and instinctively to his opponent’s moves, such as closing the gap or intercepting when the opponent first initiates. Chi-Sao training will help to progress in this. He does not think "if my opponent does this I will counter with that". Instead, he just let his limbs and his “Kung-Fu” handle the work for him naturally.
Because the range in Wing-Chun is typically so close, there is generally no time to react to visual stimuli. The art is essentially tactile, and the practitioner learns the "feel" of correct technique only through extensive drills with skilled partners. The opponent is not an object. When you see his coming attacks then your eyes will tell your brain to process the information prior to stimulating your limbs to defend and by the time your hands react, the chance is either fifty-fifty or perhaps it is too late.