Japan passed a law that states you cannot possess child pornography, how effective or how different will it be from before?

Based off this question here I wondered what would really change? Sure, the guy who would have viewed it on the loading platform waiting for the Shinkansen can’t do it anymore, but what stops him from watching it when he gets home from his 12 hour shift? The alleged rise in cases involving the production of child pornography showed that (1) there is an audience in Japan with an appetite for it, and (2) simply having laws against the production of it has not stopped it. Would it not just go underground like meth labs in the US? If a person is careful they can still obtain it, and if they make sure no one else knows they possess it, unless the authorities are going to random search people without warning or warrants, they can still get it and watch it without penalty. You can no longer legally and openly possess it, but will that really change much from before the law passage?