I mainly use it to deliberately create rivals (for duels), or to add a tiny push to plots/invites (the negative general/vassal opinion modifiers can be just enough to make someone accept an "invite to court/plot" offer).
My main annoyance is that stopping antagonising (and swaying) removes the person from the list in the outliner, even if they were starred before you started. I tend to use the outliner list as a kind of long-term to-do list, so it's rather annoying if someone disappears from the list before they're "done".