A TOEFL candidate is a person who wants to study at an American university. Now, if you have to write essays, take notes, communicate with your professors and fellow students, etc. it’s very likely that you will use a computer. So the question is how good are you at composing electronic messages? How many typos do you make when you don’t use a spell checker? If you don’t want to use a spell checker it’s probably best if you write your essays by hand and send them to an editing/proofreading service via snail mail.