This event has two major uses. First, it enables hit and run plays, especially with champions. Send Knight of Seasons or Ursa on a wild charge, then pull them back to safety. Always valuable.
Second, it helps stabilize against rushes. One weakness of the deck is that if the opponent places a unit in front of Nimid, they can keep sending wave after wave into that same spot.
While Nimid’s high health and your Guards make this strategy difficult, some assassination, focused decks may attempt it. Autumn helps you retake the flanks and secure Nimid's position.