You never go on vacation. Your family gets sick. Your friends need your help. You want to travel. You want to go to funerals for people who aren't in your direct family. You want to explore hobbies.

Idk, a few?

You're essentially designated a human of lesser value, which means nobody really cares about you. If guards harm or sexually assault you, nobody cares. If other prisoners harm or sexually assault you, nobody cares. If you get sick, nobody cares. You will not receive good care in any sense of the word. If you have mental health issues, may God have mercy on your soul.

Disregarding the lack of anywhere to go, and assuming no enemies within the prison, I see no disadvantages.