Kelvin and centigrade are the same system, but with a different zero point. Centigrade has an important place in the metric system because the system is all about ease of use and that all the units relate closely to each other. The metric system revolves around the properties of water, perhaps the most used and essential compound in nature. Water freezes at 0C and boils at 100C (at sea level). One liter (volume) of water weighs one kilogram (weight). One cubic meter (length) equals 1000 liters, and 1000 kilos or one metric ton of water. It's much more intuitive to say that the temperature today is 40C than 313 Kelvin.
Actually its completely arbitrary because it depends on one atmosphere to make sense. To every life form in the universe that didn't originate on Planet Earth, its arbitrary. But a temperature scale based on absolute zero is universal in that the only difference between the Terran version and an alien version is a scalar multiplier.
Well we haven't met any alien life yet, so ok fine. But as soon as we do, you better get used to Kelvins!
With our luck the Aliens will use Rankine anyways.
