What is Attributes To Snippet? How does it work?

The AttributesToSnippet setting is a way to shorten ("snippet") your long chunks of text to display them in the search results. Just think about the small pieces of text displayed below a Google result: it's built from a subset of the sentences of the page content, includes your matching keywords, and avoid flooding the search results page.

For example, if you limit the number of words of the "description" attribute to 10, the "_snippetResult.description.value" attribute of the JSON answer will only contain the 10 best words of this description.