2 Graphics Cards + Crossfire and 1 Monitor

So I just bought a new computer (still in route to me) and it comes with 2 ATI Radeon HD 4850 graphics cards in it using Crossfire. I don't game, but the computer will be used for extensive design work (photo and video). Also, I don't have a dual monitor setup, but I do have a high end 25" monitor.

My question are:
If I am not gaming and only using a single monitor, is the second video card a waste? Should I just give it to a friend, or will video rendering still be tons faster?
If I do only use 1 video card, will I need to do anything to bridge the two DVI connections into my monitor, or by just turning off the secondary display, does the video card do that for me?

This will be my first computer with multiple graphics cards, so any other tips I need to know would be appreciated.

Thanks.

Thank you for the info. That's the answer I expected, I just needed reassurance. I have another computer that could benefit from a better video card and dual monitors, so the card won't go to waste. Thanks.