Nowadays, when you commit a crime (you steal something of sombody or you kill somebody, for example)  you go to prison.  You have to stay there according to the judge's sentence. 

In my opinion, there are some disadvanteges. There are some people that they are in prison but they should not. I think that there are some types of action needn't to be punish by prison. There are other kind of punishment like community service or pay a fine. It is not the same to kill someone that steal a loaf of bread because you're hungry and you don't have enough money to buy it. Also, there are "popular" people due to their condition they aren't punish by prison and they have committed "crimes", like politicians.

On other hand, when the autority does its work correctly I think it's fair to be punish by prison. There are other kind of actions that a fine or a community service aren't enough. You have to pay for your acts.