A little late thought for today: When improvising a game, using recurring motives makes the game feel more sophisticated and better planned. It helps to create foreshadowing for the continuation of the game, while also creates a way to bring the story back to normal when internal consistency is broken. Motive also has the connection to higher degrees of prepared storytelling, and using it while improvising helps to create the illusion that the game is not improvised.
It doesn't have to be complicated or fancy or anything, though. It can be as simple as a kobold army that brings the forsworn doom, which comes whenever the characters failed in something and as sophisticated as a knight in rotting armour who says "the time is coming" whenever something bad is gonna happen that has an influence over a major NPC.
What about you? Do you use recurring motives when improvising? How?