A company in Texas is building a nationwide license plate tracking network. There are currently adding entries at a rate of 70 million plate/locations per month. This growing exponentially. Source.
Pretty soon, government entities and private citizens alike will be able to purchase a detailed record of where you have driven your car. What stores you have been parked in front of. A criminal syndicate could use the information to target your car for theft, or burglarize your house when you are usually not at home. Or collect information to blackmail you with.
Is it time to place a photo mask on your license plate? There are now a large number of sprays, films, and led light devices that claim to defeat cameras trying to photograph your license plate.