Spell checkers such as in Word are very useful and necessary so that you do not miss easy to avoid spelling and grammar mistakes. In fact, we think that running the spell checker is an essential step before delivering or publishing any text.
However, if you want the final text to be impeccable in every way, automatic spell checkers have certain limitations.
Why is automatic spell checking not enough? Because the dictionary is limited, it does not correct the punctuation, it does not correct the use of words depending on the context, it only knows some grammar rules, and it cannot improve the style of a text in the same way as a human proofreader.