Rockstar's new Grand Theft Auto V is so large that two discs are needed for the Xbox 360 version of the game. The PlayStation 3 version of the game which uses a BluRay disc that can hold more data only requires one disc.
The two discs on the Xbox 360 version each have their own roles. There is both a "play" disc and an "install" disc, and as the name suggests, players are required to install the install disc before they can play the game with the other disc.
Rockstar have warned Xbox 360 owners that there may be performance issues if you try to install the play disc as well. On Rockstar's support twitter account, a tweet was posted saying "For optimal performance, we recommend not installing that disc. We will have more info on our Support Site at launch." In regards to whether installing the play disc is a good idea or not.
This also means that those who want to play the game will need to ensure they have enough space on their hard drive (8GB) and if they don't they will need to go and buy one. Alternatively, you could use a flash drive with more than 8GB available storage to store the game on. To do this you'll need to make sure it is plugged in at all times while playing and choose the storage device when installing the install disc.