Explanation
Relevance Search brings the following benefits:
Finds matches to any word in the search term in any field in the entity. Matches may include inflectional words, like "stream," "streaming," or "streamed." Includes the ability to search documents found in Notes and Attachments on Emails and Appointments Reference:
https://docs.microsoft.com/en-us/power-platform/admin/configure-relevance-search-organization#what-is-releva