What do Planning Poker numbers represent?
The numbers used to vote when planning are 0, 0.5, 1, 2, 3, 5, 8, 13, 20, 40, 100. Is there a meaning when those numbers are chosen? Why don't we just choose 1,2,3,4.. for the sake of simpliness?
Answer
The point is that as the estimates get bigger, they become less likely to be accurate anyway. There's no point in debating the merits of 34 vs 35 - at that point you're likely to be miles out anyway. This way just makes it easier: does this feel more like a 20-point task or a 40-point task? Not having the numbers between 21 and 39 forces you to make look at it in this "bigger" way. It should also be a hint that you should break the task down further before you come close to doing it.