Apparently Pro brewing operations pitch way more yeast than home brewers. Mr. Malty as posted above is a much better reference than most chatter. You want your yeast to take off quickly with the least amount of stress producing off flavors and you want them to overwhelm any other organisms trying to take hold of your wort. If you go to the Doctor because you have a serious infection you don't ask for half doses of antibiotics to save a few bucks.