When a fire alarm causes the evacuation of an office tower, the evacuation and return are rather disruptive. Part of the problem is the tendency of people to return in random order, once the alarm has stopped. That means the elevators need to stop on a random collection of floors, sometimes to drop off just one or two people, before returning to the ground floor to collect more people from the throng down there.
Everybody would be better off if the throng organized itself in order from lowest to highest floor. People from the second floor could be transported first (assuming they are unwilling to endure one flight of stairs), then people from the third floor would begin moving up. Floor by floor, the entire group would be progressively transported up. That way, each elevator only needs to stop on one non-lobby floor and the total time spent by the group waiting for elevators is minimized.
Of course, as with so many systems designed to optimize the outcome for everyone, there are significant opportunities for selfish behaviour. Someone from the 20th floor could join the second floor crowd, then get a prompt solo ride up once the other people in the car have been dropped off. Countermeasures to prevent cheating could involve social pressure (shunning those who jump the queue) or technical means (restricting the elevators to move up sequentially, floor by floor).