I can imagine several good reasons, on top of the list...being involved in a hit and run or seeing something occur where you would need to remember the plate. Plate numbers, seemingly simply become painfully hard to remember in times of stress, especially if you get hit and the vehicle takes off. Say the plate out loud, the camera records the audio and now you have it for later. We all know that plate numbers are a bit hard to see on video depending on movement, angle or speed. Description of the bird turd that was driving...got it on audio....talking on the phone to your girlfriend...wife's attorney has it on audio....wait...scratch that one.