Actors hearing about their own activities

ActivityPub spec, section 7.1:

Servers MUST also exclude actors from the list which are the same as the actor of the Activity being notified about. That is, actors shouldn’t have their own activities delivered to themselves.

I am slightly confused here. In most cases, the activity will have originated locally, so the actor will be a local user; why would I be trying to federate with myself in the first place?

that’s exactly the point/intention – if an actor happens to include themselves in the audience somehow, then remove them from the list after dereferencing