Battlefield 3 gives the option for the player to install a file called "HD Content" to their storage device. This is more predominantly a matter concerning the console rather the PC, because free storage space and performance is not as much of a concerning factor than it is on the console. This install contains "extra" information about the texture and image data that already exist without the install. By installing it, the player already sees sharper edges and vivid coloring.
As you can see in the video, the HD Content is a must-have if you play with a high-definition display. Otherwise, everything is smooth, rounded, and blended, and the over-all picture quality can be referred to that of Call of Duty: World at War.
The optional install is for performance purposes, and is ultimately up to the user to install. The downside of this is that in the Xbox 360, it is mandatory that the install be to an internal storage device officially licensed by Microsoft; it cannot be installed to an external flash drive. The size of the install is 1.5 GB, and is installed from the Multiplayer disc.