Police officers are arresting people when arrest is not necessarily the best course of action. The officers are aware from the outset the result will end in no further action taken and often make matters much worse. While the police are dealing with this incident the public lose a valuable resource on the street.
The police often have to take positive action and arrest offenders for the most minor offences. More frustratingly so when the injured party has no interest in making a statement or supporting a prosecution. This is a waste of time, money and resources. The police priority should be dealing with supportive and law abiding members of society.