Schema markup, which is also known as structured data, is a code or microdata that you incorporate in your web pages to enable search engine better understand your pages and provide more relevant results to users. It helps search engines interpret and categorize information, which you want to highlight and to be presented as a rich snippet by the search engine.
The schema does not affect the crawling. It just changes the way the information is displayed and assigns a meaning to the content. So, it tells the search engine what your data means rather than just telling what it says.