To avoid the digi sending the ipad crazy. In the same way you tape the copper/silver edges on the back of the glass for the iPad Mini. You tape all the way around, making sure not to dirty the protective cover when placing back down after taping one edge.

Make sure all the metal surround is cover by tape, but careful not too go over the edges too much. It will be visible when using the device.

Like i said earlier, the real skill is not too dirty the screen when lifting the protective sheet.

Have fun!