For everyday use the unit does not matter at all. We could drop numbers completely and just say it's freezing, cold, chilly, ok, warm and hot and be done with it. For cooking we could just use simmer, boil, stew and bake.

But Celsius interacts with other units nicely. So when you actually need some precision, Celsius works nicely. Kelvin is of course the one to choose when talking about scientific matters, but Celsius works well enough for everyday things and when precision is needed.