It's a fast way to free you but the cells can be opened manually.

Before the reset, it was not allowed and was considered cop RDM, by making the prisoner respawn it delays the time citizens have in jail. So if a cop keeps killing the prisoner it can double his time. The only way you can kill somebody in jail as a cop is if they blocking the way to your cuff (2 people in one cell one is not your cuff and is blocking the way to your cuff) or if they escape the cell.