Settings: Unindexed Related Posts
Below each post we link to related unindexed posts with this feature. It helps with...
Discoverability for old content that might not have been seen yet
Fast indexing of new content
Providing highly relevant (but usually hidden) content for your visitors
This is a great feature to have on and you’ll very likely get more relevant results with it than WP plugins like YARPP (Yet Another Related Posts Plugin). However make sure you’re using a caching plugin with this feature so WPI doesn’t have to find these posts for every page load.