UPDATE: Digital Foundry, which has access to the Xbox 360 version of Grand Theft Auto 5, has offered an explanation for Rockstar's recommendation against installing the "play" disc.
"Rockstar recommends that you shouldn't install the GTA5 play disc on Xbox 360 and it's sound advice," Digital Foundry chief Richard Leadbetter said.
"When you first get the game, the first order of business is installing the mandatory content from disc one - this accounts for 7.7GB of data to install on your hard drive. Now, there's absolutely nothing stopping you installing disc two - the 'play' disc - onto the hard drive too, using the Xbox 360's dashboard to do so. It takes up an additional 7.8GB of storage. However, doing so impacts the game's ability to stream texture data, resulting in regular pop-in of in-game objects and textures.
"So what's the story here? Well, optimal streaming is achieved by making us of all the available bandwidth in the system. Why stream just from the hard drive when you can run in data simultaneously from both the disc and the HDD? Based on what we're seeing on the Xbox 360 version, perhaps running both DVD and HDD assets from just the one source slows down access times, impacting streaming performance. It's not game-breaking stuff, but it does take you out of the moment when it does manifest and for that reason we can't recommend installing the play disc.
"GTA5 isn't available for digital delivery on Xbox Live, but we are curious what the impact - if any - will be on the PS3 version, as that is available as a PSN download. The Digital Foundry Face-Off - due tomorrow morning at 11am - is based on comparison of the two retail disc versions of the game."