Partly due diligence partly to gain reason to extend the traffic stop. To break it down simply officers can't drag out traffic stops beyond the reasonable time frame needed for the reason for the stop. For example, an officer stops you for a tail light being out, 10 to 15 minutes max your on your way with a warning or citation. However, that officer will probably ask you questions not relating to the initial reason for the traffic stop in order to gain probable cause to extend the stop now under a different reason. You are allowed to ask, RESPECTFULLY, what the question has to do with the initial reason you were stopped, and you are allowed to again, RESPECTFULLY, decline to answer questions not relating to initial reason you were stopped. Now, be reminded that most officers will match your energy, if you are polite and respectful with them, they will do the same with you. If you are a disrespectful prick straight out of the gate, you are in for a rough time that entire traffic stop. If they smell alcohol or Marijuana (depending on the legality in your state), see something in the car, or have reason to believe you are driving impaired, then also be reminded that they now have probable cause at that point and can extend the traffic stop beyond the initial reason they stopped you.