In Michigan, state law requires drivers to have the registration with them, whether it is their vehicle or not, as well as proof of insurance and a valid driver's license. My own personal belief is the officer asks for all three not only to verify you have them, but also, depending on your demeanor, to give the officer another avenue of handling why you were pulled over. For instance, you are pulled over for speeding. You are courteous and promptly comply with the officer's instructions but don't have your current registration. The officer runs your plate, finds out not only is the vehicle registered to you but also that you haven't had a moving violation in more than 30 years. Instead of giving you a ticket that will put points on your record, which may also impact your insurance rates, the officer gives you a citation for not having a registration. Chances are, not only is the fine lower than the speeding ticket would have been, but so are the residual effects ie., the points and the possible insurance rate increase.
I am aware of several instances where this has happened.
Besides the license, registration and insurance proof, in Michigan you are also required to inform the officer if you hold a concealed pistol license and if you are currently carrying. That law is relatively new (at least from an old guy's prospective) and I was charged with it shortly after it took effect. Unlike most under Michigan's older and acquainted law, few people could get a carry permit for anything other than hunting and target shooting. I was one of the exceptions and had been licensed to carry for several decades when the laws were relaxed and the requirement to notify officers came into effect. I was pulled over for 5 over on my way to work one morning and after giving the officer my license, registration and insurance card, he returned to my truck asking if I was carrying a concealed weapon. Remembering the new law, I apologized to the officer and confirmed I had a firearm in my briefcase. I explained my circumstances, that I had been licensed to carry for so long the gun was as much a part of my briefcase as the pens and papers it contained, and he gave me a ticket for the speeding and let the other matter drop. Had he written me up, it would have been a fine and a trip before the CPL board to explain myself. So if you are traveling in Michigan with a concealed firearm, do not forget to inform the officer should you get pulled over.