Practical difference between indefinite criminal sentence and a definite one with parole possibility

Some jurisdictions of the US permit courts to hand down sentence ranges like “5 to 10 years”, or “10 to 20 years”. The offender is evaluated in prison and then can be let out during the indefinite period depending on how well the parole board or whatnot thinks they are doing. Some jurisdictions hand out sentences with specific terms, for example “10 years”, but permit the applicable parole board to let the person out early based on various criteria.

Is there a practical, real world difference between these two systems? If you are serving 10 to 20, and on your 11th year in prison, you convince the authorities that you no longer represent a significant threat, do they just release you unconditionally, or are you effectively on parole for another 9 years?

Are there any jurisdictions that have indefinite sentences as well as parole? E.g. person gets a sentence of 10-20, gets out of prison on parole after 5 years, then serves 6 years on parole, then is discharged after a second evaluation.