Advantages and disadvatages of a self excited induction generator?

The main disadvantage should be obvious - when the output voltage of the generator is used to provide field current to the generator....what happens if the output voltage sags? If the output voltage becomes depressed, the output power of the generator is compromised (becomes less and less), this in turn can cause the output to become more depressed, leading to an incrementally decreasing output capability.

The main advantage is cost savings.