I believe when you're given a sufficient amount of time you are able to write your thoughts clearly than when you're given a short period of time to answer questions or make an argument on an essay BUT there is a drawback with the tools within the word processing. Word processing comes with a spell check but it does not correct homonyms such as they're, their and there or other homonyms. My experience with word processing is that I always need time to effectively write something and that helps me make less grammatical mistakes when I take my time to write and edit my paper, I guess it all depends on the individual in their writing skills
I hope this helps!