It increases the speed of your CPU, therefore increasing performance. But also increases the risk of instability of your system, electricity bill, power consumption for PSU, and increases HEat. You don't need to OC with that much budget, get an i7 4770. Then you won't need any OCing with that CPU beast. If you want to experiment, you can get the 4770K version.
K stands for "unlocked CPU", it means you can OC it.