Google Search uses on-page structured data as explicit meaning for rich results
Google Search Central intro: structured data markup gives Search explicit page meaning, enables rich results, and cites publisher case studies.
Google Search can use structured data on a page as explicit clues about content—for example recipe ingredients, time, and calories. That markup can enable rich results. Google also uses it to understand page content and gather facts about entities such as people, books, and companies. Case studies cite CTR and engagement lifts for several publishers.
Based on: Intro to How Structured Data Markup Works | Google Search Central | Documentation | Google for Developers · Google Search Central