You should always use kiai, you just don't have to yell...
1) "kiai" does not equal "yell". (see my post above).
2) You should never strain your voice with a good yell. It comes from your belly, not your chest, and the throat should be relaxed. If you strain your throat during the yell, you are actually too tight and thus not using good kiai.
We don't yell with every technique either, but we strive to have kiai in all of our movements -- whether we yell or not.