On-site SEO uses whatever syntax, content logic, and supplementary files it can to make a website appear near the top of Google's generated results pages for topical search queries. When a website tries to appear near the top of SERPs for generalized subjects such as entire industries, it will naturally be facing severe competition from websites that have effectively become household names in their own right. This is primarily the domain of websites that try to be authoritative resources of information for the benefit of large audiences, but many websites instead represent businesses that merely provide services locally. This type of website can expect to be among the top positions of many of the SERPs it would appear in because local customers would be likely to search for those businesses directly.
When a website's purpose is to facilitate a local company's function to provide services to its immediate area, the snippet that is already prominently representing it on SERPs would carry out that function even better if it is uniquely structured to provide supplementary information that Google's automated snippet generation routines would omit otherwise. Local websites therefore include syntax called "schema markup" in their HTML files that essentially instruct Google to expand the structure of their snippets so that they feature information that would be useful to Google's users without forcing them to open the websites up to see this information.
Various forms of schema markup can be applied to enhance the first impressions that the snippets for different types of websites provide. For example, many service-based websites use a simple form of schema markup on each of their product or service pages to add a five-star rating system that showcases to people searching for those specific products their critical reception. Local businesses that provide services on a schedule can use schema tailored to their needs so that their websites' snippets will be accompanied by small lists of upcoming events accompanied by timestamps. As a final example, any website with a blog can insert schema into each of its posts to prompt Google to display their respective publication dates. For more information click here https://www.reddit.com/r/SEO/comments/bcy3tc/howimportantisschemamarkup/.