For the card I linked to the clock rates and voltages are the same for both bios versions but the Quiet bios has a lower flatter fan curve to keep noise down at idle and during gaming.
The Performance BIOS has faster fan speeds at idle and during gaming for those gamers that live in hot environments or are running 2x, 3x, and ever 4x video card setups (Crossfire, Trifire, quadfire as they like to call it).
The advantage is for the casual consumers and the manufacturer because The chain:
Retailer/Online retailer aka E-tailer
in all its complicatedness can stock one less product and still sell two two products worth of customers who can then just flip a simple switch to choose which way they want the product to perform. No need to stock two products, no need to learn how to use RBE.
This can keep costs down by way of distribution/stock efficiencies but also RMA issues/processes and even RMA prevention if the user can just flip the switch to get a card working again.
It also is a big plus in overclocker versions where a ODM can say we'll provide you with a card with two BIOSes
BIOS 1 = unlocked shaders and higher clocks
BIOS 2 = stock shaders and stock clocks
You can confirm stability with the stock BIOS and experiment with settings on the overclocking BIOS.
Or another scenario
Say the card has two identical BIOSes and you are a user that wants to try RBE to aggressively undervolt and slow the fan down.
BIOS 1= stock bios settings in case you make the card unusable on BIOS 2
BIOS 2= RBE version that you can edit aggressively.
Sure you can download BIOS images from the internet but isn't it nice to have a flick of the switch option to get you out of a jam in a hurry if you don't have time to fix your failed experiments? Just read a thread like http://www.techpowerup.com/forums/showt ... ?p=2129817
to see people not on top of using RBE properly.