Magic items with a mind of their own have been a hallmark of myth and fantasy for millennia. When integrated into a campaign, they can become memorable characters in their own right.
Intelligent items are a special kind of magic item that straddles the line between treasure and NPC. An intelligent item might be another type of item as well: it could be an artifact (like Serithtial on page 112), a cursed item, or even a relic that grows with its wielder.
Introducing an intelligent item is an effective way to subtly alter the party dynamic. An intelligent item works well when its personality makes it a natural complement or foil for its partner: the PC investing, holding, or otherwise interacting with the item. An intelligent item that can communicate only with that particular PC is also a great way to engage players who are a bit quieter, or those slower to speak in a scene where all the PCs can talk to a particular NPC. Due to their inherently limited agency, intelligent items are at less of a risk for stealing the spotlight than other NPCs who travel along with the party.