If executed well it seems OK, but given what we know about how well prisons are run it seems like the temptation for abuse is too great to allow.
[1]: 2:01 ~ 2:30 https://youtu.be/AjqaNQ018zU?t=121
RA’s (Resident Advisors) at American universities, students whose job is to handle dormitory issues, are compensated via free “room and board.”
The state has chosen to imprison these people, it is forcing them to live inside the prison. The costs the state incurs in maintaining the prison are not "paid room and board" for the inmates.
Whatever crime you were committed of did not carry a penalty where you had to pay for your housing in prison. So your room in board is covered in the case where you work and where you don't and can't be deducted from wages. Now, the crime you were convicted of may have required you to pay some form of victim compensation. This is often deducted from any prison wages.
and don't forget healthcare.