The spirit shout is great if you have a one time all or nothing breaking the board kind of situation. However, if you are in a confrontation, I don't advise doing a lot of yelling. It tends to disrupt the natural breathing pattern. We break boards and hit makiwara and spar and grapple and never, ever do we do a Hiyaa! I can focus my energy by relaxing with a slow exhale during the strike.
Most point sparring gurus only do it to attract attention for a particular move for the judges. judo teaches it for falling. I know how to fall without yelling.
But hey, if you wanna whoop it up, feel free....
I know Mushi yells a lot when I smack him around.
SZ