Why might it be 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 degress 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 degress celsius :).

And a) oxygen i believe