Consumption and carrying small amounts is tolerated, police will not take any action and public attorneys never prosecute these cases.
But production is illegal and besides two small plants in your home, completely not tolerated. If you get caught with say 10 plants they're destroyed with few other consequences. If you get caught with a more considerable production however, you get prosecuted.
A lot of softdrug related crime isn't connected to consumption but rather production. The Netherlands isn't a good case study for studying effects on that kind of crime etc.
Same with many other drugs like xtc. Consumption is rarely criminally targetted. Production is. Virtually ever farmer in the south of the country gets approached by drug producers, there's a whole undergeound web of crime, black money, corruption etc.