Structured data earns rich results in classic search (FAQs, stars, breadcrumbs, product info) and gives AI engines typed facts — names, dates, prices, authors — they can repeat safely. It's embedded in a script tag and never changes the visible page.
The core rule: markup must match visible content. Google treats schema that claims things the page doesn't show as spam. The practical minimum for most sites is Organization and WebSite everywhere, Article/BlogPosting on content, FAQPage on question-answering pages, and Product or SoftwareApplication with Offers on commercial pages.