They are not required in my school, but I have one. They are very useful in geometry & algebra classes. For example, in geometry, with some postulates/theorems you need to get the answer, but you cannot use any rounded off numbers to get it. It is a lot harder and longer to do it with fractions, but if you have a graphing calculator you can use the 2nd->store feature to save a number. You can set that specific number to a character on the calculator, so you just type in that character in the formula, and it will replace it with that number. Kind of hard to explain lol, but they are quite useful
