Why is it whenever police are about to apprehend a suspect in the street, they shout to them from about 50 yards away, enabling them to run off instead of waiting till they have approached them?
I think it gives the suspect a chance to comply - failure to respond, or to respond with rapid movement in the opposite direction is an offence, and the suspect, when caught, can then be arrested and taken to the station for questioning.
Of course, if you are talking drama, rather than documentary, then making a noise and starting a chase is simply more dramatically effective than having the proverbial 'quiet word'.