More rotors = more lift, more rotors also make a craft more stable, Pro level Aerial drones often have more rotors for lifting heavy cameras. Another advantage of 6 or more rotors is the fact that some crafts can still fly if a motor or ESC (electronic speed controller) decides to stop working for mid flight, While it’s not ideal most crafts with this amount of rotors can usually make it home, this is not the case with quadcopters.