For those of you who are unfamiliar with the practice, some beekeepers cut off part of the wing of their queen. There are at least three reasons for this. First, it will keep the colony from swarming. Secondly, it can indicate the year of production of the queen, and finally, it can be used to mark a particularly valuable queen.
The idea behind swarm prevention is that when the queen is cut, she will not be able to fly. When the swarm realizes that the queen is not with them, it returns to the hive. In the short term, this may buy you some time. But the colony retains the impulse to swarm even if the queen cannot come. In the end, the swarm will go anyway, maybe with the virgin queen.
Some beekeepers mark the age of the queen by cutting off the right wings on even years, and the left on odd years, with the explanation that when the color disappears, information is lost.