The card has different profiles or performance modes with different clock values for each. The card should switch properly between them, depending on gpu load and whatnots.
For example (gpu mhz/vram mhz): Low (150/300), Medium (400/600), High (900/1200). This app, simply would simply make Low and Medium be equal to High. So the card would run at (900/1200) all the time. (The overdrive tool in CCC to overclock the card, affects the High profile only)
In emulators, the logic for changing profiles can get very confused it seems, since sometimes you'll get a lower profile than you need (or even never get the high profile triggered) and actually have lower performance.
Would this help Dark Souls? No idea. If the game already triggers high performance mode, then it won't have a difference. You can see your current clocks with tools like gpu-z and the like.