on Writing Forward:
When we’re writing, we run into a lot of technical issues. Where do the quotation marks go? When is it correct to use a comma? How should titles be formatted?
Some of these questions are answered by the rules of grammar, spelling, and punctuation. But other questions are not addressed by grammar: there’s no official rule for how to format a title.
We writers need trusted resources that we can use to resolve all these issues, especially if we want to produce work that is both grammatically correct and stylistically consistent.
That’s what style guides are for. Style guides answer grammatical questions and provide guidelines for consistency.