Short volatility

The VIX index is a measure of equity volatility, of the S&P 500 index. It is investable through VIX futures and ETF’s, or via options. People buy volatility to hedge their equity portfolios, because high volatility is associated with equity market crashes. The way to invest in the VIX is then to take the other side of these buyers, and sell volatility. While this gives you a good return you are now exposed to the risk of equities crashing. So it is not clear that it would be valuable to have both short VIX and S&P 500 in a single portfolio.