So domains are recursive tree structures. So u have node com which has a bunch of nodes below it of different domains which can have sub domains etc. Its like this cos that’s how DNS was designed.

Search engines gives scores to domains and pages. When u say that the content origin of ur page is some other domain the search engines will use that knowledge to adjust rating accordingly.

Say u have 2 domains site1.example.com and site2.example.com the search engine with l have a rank for site1, site2, and example.com where the rating of both site1 and site2 effect the rating for example.com.

If the content origin for all federated content has the same origin say instance.fediverse.com then the rating for all federated content will be classified as part of fediverse.com and all content will be working together across all instances boosting the fediverse as a single entity.