Why is it important to know what temperature scale is being used in a given situation?

It depends, for example, it is quite important to know the Kelvin scale (i.e 0 degrees Celsius is 273 K and -273 degrees Celsius is 0 K ) when dealing gases. But I don't know other situations where you would need to know other temperature scales.

Hope this helps and also if you are using Fahrenheit 1 Fahrenheit is -17.22 degrees Celsius 

The real answer is keeping the world healthy so we won’t die