Some times it's so they can call something fat free or low calorie, for example, if it has a half gram or less fat per serving, it's fat free.
So if some portion has just under a gram of fat, they can call that two servings, and call the thing fat free.
The government just says the serving size has to be reasonable or something like that, you can't make butter 7,000 servings per container and call it fat free.
My absoulte favorite is the half gallons if ice cream. 14 servings per container (they are actually a bit less than a half gallon now, that's why it's a weird number like 14)
Does anybody really get 14 servings from that?
Or 2.5 servings of soda from a 20 ounce bottle?