Justin, yes it is useful to law enforcement. First most police vehicles are equiped with cameras which should be activated prior to going enroute to a call, then the video can be reviewed on a monitor for suspect(s) leaving the area. Sometimes the officer has no idea who or what car he is looking for until he gets to the call and talks with the victim, he may than learn that he saw the suspect/vehicle while enroute. In any event an officer, if he has suspect vehicle information can look at the front plate as he approaches the scene. They may be hard to see (license plates) on the freeway or at high speeds, but not in cities at 25 - 45 mph, they can be very useful. Although I am not an advocate of "photo radar" they are useful for those purposes as well. (side note - where I worked we did not use photo radar as our department did not agree with this type of enforcement)
If this does not answers your question let me know as I can give more examples but did not want to bore you with a book.