1. We can use this function to pass a flag to indicate if content has blocks when we have decoupled environment, where WP is backend and frontend is implemented in some other language.

2. We can convert (parse) block output as per our requirement and pass it in the API. While, converting it can be useful to check if the content has any block. This will let us pass content efficiently by implementing parsing when it is necessary.

class WPDocs_Custom_Block_Parse {

	function parse() {
		// Do something
  	}
}

function wpdocs_custom_block_parser() {
	return 'WPDocs_Custom_Block_Parse';
}

/**
 * In the implementation check if content has block
 */
if ( has_blocks( $post_content ) ) {
	add_filter( 'block_parser_class', 'wpdocs_custom_block_parser' );
	$response_content = parse_blocks( $content );
	remove_filter( 'block_parser_class', 'wpdocs_custom_block_parser' );
}