Pretty much what @carrieseltzer wrote here (Carrie or a site admin, please correct me if I’m wrong):
-True coordinates of observations that you have chosen to make obscured or private (via user-selected “geoprivacy”), if you have affiliated your account with iNaturalistFi.
So if you’re affiliated with iNatFi, made some observations in Finland and manually obscured or made them private, the folks running iNatFi will periodically have access to those coordinates.
If you make observations in Finland, are not affiliated with iNatFi, and those observations are obscured due to taxon geoprivacy (you don’t manually obscure or make them private) the true locations for those observation will be periodically available for the folks running iNatFi.
By affiliating with your local network site, you can receive updates about relevant iNaturalist-related news and events.
You might receive some communications from the folks running iNatFi if you are affiliated with it.
Otherwise it won’t really affect the user experience unless you use that network node as your main entry to iNat. iNatFi is in Finnish by default, has its own logo and color scheme, search results are restricted to Finland by default, etc.
This is also explained in the iNaturalist Network Affiliation in your Account Settings page, and if you want to dig deep, here’s more about running a network node: https://www.inaturalist.org/pages/network-join