MMI is a sentiment index, so buy/sell decisions should not be solely based on the current value.
But once the decision to invest or close existing positions has been made, the MMI can help in timing the market better.
A high extreme greed value (>80) suggests investors should be cautious in opening fresh positions as markets are overbought & likely to reverse.
A high extreme fear value (<20) suggests a good time to open fresh positions as markets are likely to be oversold and might turn upwards.