Realized volatility, but why?

A Quick and "Dirty" Volatility Estimator for Option Traders

Option traders often need to estimate volatility quickly and efficiently. While many brokers provide realized volatility based on close-to-close data, this method, though reliable, converges slowly and is relatively inefficient. For those seeking to incorporate daily range (highs and lows) into their volatility estimates, the Parkinson estimator offers …