if i remember correctly, the high power ones make it brighter (obviously) and keep it from having "hot spots" or spots that have more intense light than others.
i might be wrong. but i think i am right
anybody else, please feel free to correct me.
Tha Kraken: http://www.focusfanatics.com/forum/ford-focus-builds-general-showroom/285082-meet-kraken.html