Serves absolutely no purpose in both single player and online. I remember there was a lot of talk about it in the few months build up to the game, about the possibilites about maybe being sent to prison or possibly 'prison break' type mission series. But no, absolutely no missions take place in - or even near - the prison, and there is no other reason to go in there either, can't enter any of the buildings and there's basically nothing in there, just a wanted level.
A lot of people also thought that it would be kept for online play, along with dozens more shops and building that we would be able to enter (lol yeah right). Rockstar really missed an opportunity in my opinion.
Are there any other places on the map which you think were also vastly underused in both missions and also general gameplay potential?