This is nice when you want to let a group of people collaborate on the curation of a river.
Also makes it possible to use Fargo to edit subscription lists. Just edit the list in the S3 bucket to contain a node that includes the Fargo list. The editors don't need to have access to the bucket.
I needed this feature for a project I'm doing where the curator is comfortable editing OPML lists, but isn't ready to make the investment in learning how to operate a river.
It also makes it possible to switch the river to another server without changing any update procedures.
We only go two levels deep. That is you can have an include in the top-level subscription list, but any includes in included lists are ignored.
The only reason for having this limit is that it eliminates the need to have a stack to make sure there's no circular recursion.