This charm is used to send/share data to the peripheral devices connected to your system. A peripheral device may be a secondary monitor of a dual-screen setup, a printer, sound system, a TV connected to the machine, etc.
I opened a webpage in Metro Internet Explorer and summoned that Devices Charm. It shows me the above shown 3 device options that IE can “talk” to:
Another example might be of a video-playing application. In that case, the Share Charm will offer to play video on a connected TV instead.
This charm would mostly be used to print, send and play content. The main advantage of this charm is that the app will know what all connected devices it will be able to use. It also eases the user’s access to those devices in an intuitive manner.