It is used by police interrogators to have a subject incriminate himself without realizing it, and more importantly, without speaking further about the topic. It exploits a known phenomenon where people focus on the most recent topic. By quickly shifting to an unrelated topic after something incriminating was said, the interrogator can avoid having elaboration to elaborate on the statement, and to avoid protest from the subject.
It is noted that politicians are also aware of this technique. By creating a new topic of debate, focus can be shifted from a more incriminating one.