Hi! Glad to meet you here, for I'm planning to take TOEFL too. Apparently, my English is not good enough to correct your essay, but I have one suggestion for your essay.
When it said "Do you agree or disagree with the following statement", I think the first thing you should do is to answer its question, that is to take a position. However in your essay, it was not quite clear that whether you agree or disagree with its opnion, but started to anwser why it's important directly.
To me, this topic is indeed a tough question. Actually, the first thing I want to ask is: how do you define "useful"? And this was becoming a truely philosophical question. But if I wrote my essay like this in TOEFL, I'll be dead. For they will say this is "off the point". In TOEFL, they simply expect you to write like a elementary student. What a shame!