This is not the case with all karate styles, though. Heck, the words I repeat the most during the classes are "relax" and "move" And I can never emphasize enough that you have to be "with", vs. "against", your opponent. Back to the original question, I think what matters most is to move out of the "danger zone". And you don't need to move by much ! If your timing and distance are right, a simple shift of weight to the back is enough. Applying the same principles, we also practice moving in, and aside at the last moment - this is irimi, and this is extremely confusing for the attacker since you deliberately give him this target, to better take it away at the very last moment. Whatever the technique, the key point is to do it timely. Doing it too early is just as bad as not doing anything, because the attacker with follow you. So you have to move out only after he has fully committed his body into the attack.