I can think of a number if situations in a number of jobs I have had were people following me around could have been dangerous (farm hand, concrete work etc).
But - in my opinion obviously - if following even someone like me around might be dangerous in certain situations then definitely I can see how it might be dangerous to follow police around?
That said, I am not saying you shouldn't be allowed to folliw police at a safe distance, at a safe speed, recording what you see etc as long as it isn't obvious that they are doing something that temporarily needs to be kept secret.