No, its drug use has not gone down, nor has the rate of crime gone down anywhere proportionate to the growth in the rate of incarceration.
Number two, they do clog up the court systems.
Number three, they transfer discretion to prosecutors and police officers, but surreptitiously. They do not have the intended effects on the discretion of judges, because in the international evidence, judges and prosecutors surreptitiously subvert the mandatory sentences in order to ameliorate the harsher consequences.