I am not sure about your question, so see below.

If you are asking about how/when to use warcry:

You should use it just before your units engage (seconds before). Regardless of the actual effect regarding stats, it increases the effectiveness of the unit in combat.


If you are asking about the technical effect of the warcry on the stats of the unit/nearby units:

I could not find another thread here at the ORG, but found on other sites the assertion (unsubstantiated) that the warcry increases Attack value of that unit by 10 for 30 seconds. No statement regarding morale. No apprent effect on other units.

If anybody has first-hand information regarding this, or a reference, it would be appreciated.