Prisoner self-provisioning, whether in govern run or privately operated facilities, require prisoners to grow and produce their own food. It is much cheaper for taxpayers to provide the "starts" for growing their own sustanance. In growing and providing for their own sustanence, we are also educating and training them in job skills.
Reduces costs for support of prisons and prisoners. Increases job skills of prisoners and potentially supports their transition back into a productive society.