"Do you want to spend an hour doing correspondence, putting a person through the court and get a minimal sanction for an offence that happened under the influence of alcohol at two in the morning?"
Those issued with a pre-charge warning are often first-time offenders who deserved a second chance, the commissioner said.
"It relates to those who don't have outstanding warrants, who don't have previous warnings, who have a right be given a second chance.
"These are people who do something silly, invariably under the influence of alcohol, and they are fingerprinted and photographed. They may spend some time in a cell. There is that sense of sanction.
"It doesn't send a message they can get away with it ... We don't see that as a soft option at all."
The arresting officer has the discretion to issue a warning, but it is usually used for offences that carry a penalty of a six-month sentence or less.
"Recidivism is being monitored ... and it's not large at all," Mr Marshall said.
But he did not have any figures for people who had received more than one warning, or those who had gone through the courts after receiving an earlier warning.
Sensible Sentencing Trust spokesman Garth McVicar said he had no issue with the warnings, as long as police kept a record of who had received them.
The warnings are part of the policing excellence model that includes a number of initiatives to increase the presence of officers in the street.
Others include rostering more police to work when demand is expected to be higher and greater use of mobile technology to allow officers to issue infringement notices without having to return to a station.
SECOND CHANCE
* Police issued about 19,000 pre-charge warnings from September 2010 to November last year.
* This led to a 9 per cent reduction in charges in the district court.
* The warnings are given for arrests for low-level crime that do not lead to a prosecution.
* Half of the warnings have been for breaches of liquor bans and general disorder.