@crazycells That's a good question, and not one I'm sure I have the answer for.
It's something I wonder about because it has been said that search engines will penalize sites that contain repetitive content. Does that mean we may see downweighting because federated content can be found word-for-word elsewhere? I don't know.
I think what might be a good practice would be for a site to refer back to the original site if available.
For example, if you inspect the source for this topic, you'll see that it contains a canonical reference:
<link rel="canonical" href="https://community.nodebb.org/topic/17867/pre-alpha-activitypub-related-bug-reports?page=3" />
If this topic appears elsewhere (and it does, on the ActivityPub SocialHub), then it would be better if that site also provided a canonical reference back to community.nodebb.org, but that's not a requirement anywhere at this point in time.
That way, a search engine upon encountering a site, would be able to learn the appropriate original source and weight it accordingly.