The parole board is a gamble to some extent, but it's better than the alternative. No possibility of getting out early eliminates the need to be on your best be

The parole board is a gamble to some extent, but it's better than the alternative. No possibility of getting out early eliminates the need to be on your best behavior in prison, which creates a bigger management nightmare. So you sentence someone to 2-10 years and the idea is if they behave they get out in 2 years. If they don't behave, they will have to try again each year to convince the parole board they are no longer a problem, or if they never get their act together then they are released at the 10 year mark (this is called maxing out). Oftentimes for non-violent crimes they get their parole automatically at the minimum time without having to see the parole board, unless they became a management nightmare in prison.