How many people each year get charged and convicted of possession of cannabis? Police care about possession, they care about supply/distribution/dealers.
Leaving it up to police discretion is a bad idea. It also seems to disproportionately affect Maori. According to the Ministry of Justice, the police arrested and charged 3101 people in 2019/2020 for simple possession or use of cannabis. This figure excludes those arrested for cultivation, supply, possession for supply, dealing, distribution, etc. It is only for personal possession and/or consumption.