Rockstar does not recommend that anyone installs the Play disc from Grand Theft Auto V on Xbox 360.
Grand Theft Auto V on Xbox 360 comes with two discs, one being the Play disc and the other being the Install disc, Rockstar does say not to install the play disc for optimal performance, there will be more info on this on Rockstar's support site at the launch of GTA V.
For anyone who remembers, Halo 3 also had this aswell where Bungie also said not to Install the game as it made it slower with loading times.