Overclocking can increase the performance of the card, but it can also damage it. It’s something that if you don’t know what it is, chances are you don’t need it.
I only overclocked mine cause I wanted to pull everything I could out of the computer. I built the computer to be a speed freak. It loads Windows 7 in roughly 2 seconds and plays just about any game I throw at it at 60 frame a second (max graphics, in HD) while running iTunes and a web browser on the 2nd monitor. I doubt you need that kind of performance all the time so the way the card is now should be fine.