volatility is the de facto measure of risk for a portfolio/trading strategy (there are more measures but vol is common). People tend to measure performance on a risk-adjusted basis (for example the Sharpe or Information Ratio) because in an ideal world an investor could theoretically lever/delever a portfolio to a level of risk they are comfortable with. All things being equal a higher Sharpe ratio would give you more returns for the same amount of risk as a portfolio with a lower Sharpe ratio.
