When launching a new Lemmy instance, your All feed will have very little populated. Also as a small instance, new communities that crop up may never make their way to you. LCS is a tool to seed communities, so your users have something in their All feed, right from the start. It tells your instance to pull the top communities and the communities with the top posts from your favorite instances.
How to run manually and in docker is included in the repo.
Let me know if there's anything anyone needs it to do and I'll see if I can fit it in. I'm going to work on a "purge old posts that are unsaved and not commented on by local users" first, since small instances are sure to run out of disk space.