It's simply for covering the back of the computer, and for shielding your inputs and outputs from being jarred around and damaged when you're plugging in and unplugging things. Some people on this thread seem confused. Because it has "shield" in the name, people think it's shielding against current or EMF. It has nothing whatsoever to do with current, or EMF interfering with radios or anything else. I use radios, I also have no covers on my computer, side front or back. To add to that, the radio I have right now is inside my computer. It's really only aesthetic, there to look good because as a shield for your inputs and outputs most of them are fairly useless without being actually attached to the board and solid rather than thin and flimsy.

The shield's main job is to protect the pc from dust, and it also makes the rear look a little better if that matters to you.