It is NOT a ninja weapon, as many people believe, as it originated outside of Feudal Japan. Also, the term 'nunchucks' was coined by the Americans after discovering the weapon, but it is an acceptable name for the weapon.
The major disadvantage of the weapon is the possibility of an opponent catching the weapon in his hand/s and pulling it out of your hands, leaving you disarmed.
The common strike method is the wrist snap, spinning the "chucks" around the pivots in the chain, striking your enemy multiple times quickly.
In the right hands, these can be effective weapons, however more often than not they are more of a danger to the wielder than anybody else. Even so, owning this weapon is strictly controlled or prohibited in many countries.