Free will has a lot of different interpretations. For personal life I find this one the most practical: if you have the impression that you have free will then

Free will has a lot of different interpretations. For personal life I find this one the most practical: if you have the impression that you have free will then you have free will. Even if your choices are in fact determined rather than choices, the fact that you think you're choosing makes the determination irrelevant. Judicially the argument goes exactly the other way: unless we have proof for free will any punishment (for possibly predetermined decisions) is unjust. The justice system then only serves three possible functions: 1) keep dangerous people away from society 2) act as a deterrent, a factor that goes into any predetermined decisions and 3) to help rehabilitation, help the individual make better choices. The justice system eg in Norway very much fits these schemes, while common people still see prison etc as punishment the actual judicial decisions much more aim at rehabilitation.