For the real serious offenders that have committed really Horrendous crimes such as murder with no remorse and are a real threat to our society then I think that they should not be given good credit and get out sooner.
They should rot in prison until they die.
But for those that have only committed crimes such as money laundering, break in's and other theft then if they get 20 years in prison and get out sooner because they've shown to have good behavior and won't be a threat to society then I think it's okay to release them early.
People can and do change and I think some people should be given a second chance at life out of those bars.