Sorry for my ignorance, but how does this work please and does it damage your pc or void warranty? If you can overclock your pc, then why doesn't it ship with the overclocking already done.
Computer hardware needs to be reliable and stable so every product will be manufactured with specifications that allow that goal to be reached. Overclocking a product can cause instability and in worse case scenario even a mailfunction. Overclocking will generate more heat and will consume more power so you may need to make modifications for computer cooling or buy a better supply.
Many videocard manufacturers have factory overclocked cards that has been tested and designed to be stable even when they are overclocking the GPU beyond default Nvidia/Ati specifications.