It would be useful if you live in the United States, or any of the dozens of countries that use the system either as a standalone measurement of temperature or as part of a dual system. The British Virgin Islands, Antigua, Barbuda, the Bahamas... Etc.

I find it actually kind of a fun way to start a conversation with anyone outside of the U.S. by attempting to convert my local weather to Celsius. I'm on international calls fairly regularly and (can't blame anyone for this) telling anyone outside the US or the countries above the temperature in fahrenheit is like speaking a foreign language.