Bans do a hell of a lot for those who aren't willing to risk the consequences of theft or manufacture and don't have any social connections beyond immediate family, even for targeted bans on a specific population of something which is incredibly prevalent such as alcohol can be incredibly effective to the point of denying a desperate man access to his vice for years or even decades. The only reason bans get a reputation of ineffectiveness is because of non-whites who will somehow find a way to access it regardless.