While spell check and grammar check are valuable tools and often catch obvious errors, they are not capable of picking up nuance.

For example, if one uses effect when affect should be used, spell check often will not distinguish. It might also miss the use of an incorrect form of a word, e.g., they’re/their/there.

Spell check and grammar check should always be used, but they are not foolproof and careful attention to detail is still required.