Checking your work is crucial. How embarrassed would you be if you said butt instead of but in your essay for charms? That wouldn't earn you a great grade. So it is very important to check your work. Spelling and grammar mistakes aren't the only thing to look out for. What if you got an answer wrong? Or you wrote a potion ingredient in the wrong spot? Re-reading your work is CRUCIAL! I don't know how many times I have to say that! So double and even sometimes triple check your work. You don't want an embarrassing or obvious mistake slipping through unnoticed. That is one of the things professors or PA's grade on.