Currently, federal inmates (219,000 of them growing at a rate of over 6,000 per year) have an ability to earn "Good Time" for each year they are incarcerated. The current Good Time earned by an inmate is 54 days per year for being, well, good. Nobody wants another day added to their sentence, nor does an inmate want to call home and tell the family 'I got caught smoking pot so I won't be home for another month or two'.