Currently, wikibase clients will trigger a purge of an item's connected page if any sitelink on that item changes. However, that purge is only needed when a sitelink that is actually shown in the page's sidebar is changed. This is the case for all wikis in the same family (inter-language links) and all wikis in the same language ("sister" links) - e.g. German Wikipedia would show English Wikipedia and German Wikivoyage, but not French Wikivoyage or Italian Wikinews. Ignoring changes to other sitelinks should help reduce the number of page updates triggered by wikibase changes.
In, AffectedPagesFinder::getChangedAspects, when sitelinks are changed, only trigger the SITELINK_USAGE aspect if the sitelink is either in the same family or the same language group as the local wiki.
This requires a re-interpretation of the //S// usage aspect: it then means usage of "sitelinks used in the sidebar", no longer "use of any sitelinks". This means that explicit usage (via Lua) of other sitelinks needs to be tracked as //O// (or //X//).