I have gotten to the point where I rarely voice a kiai at all. My understanding is that it's a Japanese thing that has mutated for the purpose of theater in competition. We've all seen clips posted here that show some extreme, drawn out, face-turning-purple-kiais... useless, of course, in application. After doing one of those kiai's, you would be so out of breath you couldn't continue to fight! Should be short and explosive.
Osu, we've all seen it and in some circles that is what is rewarded in competition. Of course if that type of kiai was used during a fight, it would not serve any practical function I can think of.
I do think kiai's are important for various reasons. These are a few off the top of my head:
1) Helps focus power and coordination during tameshiwari. Sure you can still break things if you didn't kiai but I have found that releasing the kiai at the moment of impact is like a fulcrum to complete the break without any seeming injury. Could entirely be just my perspective and I haven't tried to do any serious breaks without a kiai so perhaps my data is not quite empirical.
2) When teaching kids, I sometimes use it as a gauge of their interest and commitment to an exercise. Having a strong response in the kiai's seems to encourage the group to work harder and be more in synch.
3) It's an audible response to being struck or striking so we can see if the timing and implementation of the kiai is being used as it is intended. In the case of being struck, we use a short and explosive kiai to expell the air from the body to help brace for the impact and to make sure muscles are tightened at the moment of impact. In the case of striking, the kiai is also short and explosive but where it is of most benefit is to verify timing with strikes with breathing. If the kiais (breathing) are not synched with strikes that there is something off with the timing.
Typically, we go into "low" stances, whether its zen kutsu or shiko dachi, only when executing some sort of grappling or pulling technique, to lower our weight for balance, leverage and power. Most of the time we are in a "stand up" striking stance closer to boxing - feet more under the body
Very interesting and makes complete sense in that context. Our zen kutsu dachi that we practice is low but not the lowest. We try and keep the front leg thigh parallel to the ground but without lifting the back foot as to have sokto off the ground. Moving in zen kutsu dachi in this manner is a leg building exercise for us that also allows us to practice kihon and renraku.
We rarely use shiko dachi. It is typically used in stretching or as a variation of kiba dachi but the frequency is not that often.
Our 'stand up' striking stance is called kumite dachi simply enough and resembles what you describe as well. We're certainly on chusoku for the most part with balance and movement that allow punching as well as kicking. Of course if it was that simple, everyone would be great at it but the long and the short of it is that it takes time to understand the concept and even more time to be able to implement it in your game.
In any event, thanks for the share.