At retail, they call it the final foot before closing the sale. The consumer is alone on a shopping aisle. Just 12 inches away from the product on the shelf, and anything will help close the sale.
In travel, agents have a far greater advantage - you can close the sale with even a minor incentive. It can be an extra tour. A cabin or room upgrade. Wine with dinner on a tour. Even a special car service to the airport to start the trip.
In this environment, a consumer really wants the vacation this year. So agents really have to be entrepreneurs in closing the sale.