How does that help? It’s like identifying in which continent a picture was taken.
Police aren't going to go around pulling over every one of those cars. However, if a suspect is captured, it can be a datapoint to help make the case.
The paper talks about using this to go after people who are creating CSAM. That's a federal crime, which means an investigation will be conducted by federal agents. USAs have a 93% conviction rate – they'll case build like crazy to ensure they get a conviction. Any data point helps.
Plus, they might ask you if you took a photo with your phone – say "no" and they prove you did, and you're also lying to the feds, which is a felony itself.