Just like learning to play a musical instrument, muscle memory is built by repetition, and doing something wrong during that repetition ingrains it into your mind. It is much more beneficial to do it right the first time, than training the bad information out later on.
.
In the martial arts, faster is usually considered better. Performing a faster kick or punch can be advantageous, and you will see students in the dojo trying to improve their techniques, concentrating on punching and kicking faster.
.
Fast, however, can also hide a lot of problems – especially bad technique. When I watch students, too often, there are poor biomechanics – elbows moving outward, shoulders rising, the knee and ankle out of line – things that can dramatically reduce power and efficiency.
.
That’s why sometimes its good to practice to “slow” down. Simply, what this means is that you should practice your techniques very slowly, while intensely focusing on what and how your are doing it, paying attention to correct bio-mechanics, balance and form, trying to eliminate any errors of technique.
.
Often more experienced students can have difficulty correcting their form – they have integrated their technique into muscle memory so much, that unless they are really concentrating on what they are doing, in terms of improving their technique, they just revert to what they have been doing all along.
.
If you sometimes incorporate “slow” practice, your technique can improve, unnecessary movements can be eliminated, and you will learn to better keep your balance through progressions of movement. Your technique will improve and you will become stronger and faster….. the very thing you were aiming for in the first place.
.
Training slowly is also about conditioning of internal muscles that are part of larger muscle groups, tendons, and ligaments; including the synaptic control of them. This requires mindfulness – intent and focus, as well as repetition. This is internal karate.
.
Take, for example the many stances we use. We train students to do them correctly by putting them in a frozen position, sometimes holding the pose longer and longer – extending the posture deeper and wider. However, we never hold these positions in a real fight! They are transitional, flowing from one to the other and staying in them only long enough to unbalance an opponent, close/open a gap, slip their attack, execute a throw, etc…… Balance is the goal in all things.
.
Practicing “slow” builds the proper foundation….. it does not however teach the proper application. Application without foundation is weak karate. Foundation without application is just dancing….. 
.
“You may train for a long time, but if you merely move your hands and feet and jump up and down like a puppet, learning karate is not very different from learning a dance. You will never have reached the heart of the matter; you will have failed to grasp the quintessence of karate-do.” – Funakoshi Gichin
.
.