What purpose does the IO shield on computers serve? I have been reading a lot of articles (mostly forums) on the internet and can't seem to find a definitive answer.
1) Shield to keep electro-magnetic radiation inside of the case
2) Dust Cover / Air circulation director: The fan in the power supply shall draw air throughout the entire case and not just along the short way from the I/O area to the power supply that's usually right above.
3) Aesthetics: No ugly hole.
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.
For posterity's sake, I'll add something new, here. I'm finding this thread in 2017 after typing the question into Google.
Before now, I've read a few POVs stating that the IO shield isn't necessary at all. In fact, I went to a parts shop recently after losing mine assuming it was an absolute requirement. I was set to buy a replacement motherboard, because I couldn't find a replacement IO shield anywhere. (I admit I was an idiot). The rep at the counter told me not even to bother with the IO shield and definitely not to buy another motherboard from him.
He told me that IO shields are included so that motherboards can pass inspections in some countries. Some countries have strict "no exposed components" policies. If a mobo ships without a shield, then the manufacturer is forcing the recipient/builder to leave components exposed via the IO hole in the back of the case.
So, it might be overkill. "No exposed components" might be a policy designed to make sure that mobos, GPUs and the like are properly housed. That little hole in the back might not be dangerous, practically, but technically it violates the code outlined by the policy. So IO shields.