Tag surrender

Why returning plates should be important to you:

Financial Responsibility sanctions can occur once insurance is dropped from the vehicle if the license plate is still actively registered and associated to your vehicle. Failure to surrender a valid license plate when your insurance is cancelled or expires will result in suspension of your driver license.
When you dispose of a plate by turning it into a tax collector's office you will receive a receipt showing that the plate was surrendered. If the initial registration fee was paid for the vehicle that the plate was on, that receipt can then be used for credit towards a future vehicle registration to keep you from paying the initial registration fee when you purchase a new vehicle.
So that scammers do not attach your plate to their vehicle and go through tolls, red light cameras, or be used on vehicles that are part of a crime. When this happens, the name and address on file will be yours.
Link for additional information on tag surrender.