The Auto Cashout feature in 'When Moon Bro' allows players to set a predetermined multiplier at which they would like to cash out their earnings automatically. This means that if you've set your Auto Cashout at a certain level, the game will automatically cash out your bet when the multiplier reaches that number. This feature helps players manage their risk and can add a strategic layer to the game, as you can decide your exit point based on your comfort with risk and potential reward.