It depends. If you install a discrete video card you can do hybrid crossfire. This will use both the integrated graphics and the dedicated graphics. However you can only hybrid crossfire up to a Radeon 6670 any higher video card will disable hybrid crossfire. Also if you use two seperate discrete video cards in standard crossfire that will also disable. You can also use the integrated graphics on it's own as you would with an Intel CPU.
Apparently I didn't word my question understandable enough. I know about Dual Graphics. I was asking if the on-die GPU was used for any other purpose than rendering graphics. If I went with a discrete card instead of using the on-die HD 7660, would the on-die GPU be turned off, or would it still be of some use in other data processing?