Question: what are the value of style guides and style sheet?
Answer: improve communication

A style guide establishes and enforces style to improve communication.  To do that, it ensures consistency within a document and across multiple documents and enforces best practice in usage and in language composition, visual composition, orthography and typography. For academic and technical documents, a guide may also enforce the best practice in ethics (such as authorship, research ethics, and disclosure), pedagogy (such as exposition and clarity), and compliance (technical and regulatory).