Another example of rule by a few is oligarchy. This is where you have a small group of socially and economically elite citizens that are essentially making all of the key decisions. Oligarchs usually make decisions based mostly on their own interests rather than for the general good. We see this often in situations like in China, when the Communist Party ran the show and the leaders of the Communist Party made decisions for China based on their own interests and not necessarily the greater interest of the Chinese people, or in situations where the oligarchs are based out of the military, and they let the military run the government.
Another example of rule by a few is plutocracy. This is similar to oligarchy, but when you hear plutocracy we're talking specifically about rule by the rich for their own benefit. This became one of the big problems that faced the Roman Republic in the 2nd century BCE because it was the most wealthy Romans that were running the Republic for their own benefit, and it wasn't the egalitarian system of government that many Roman citizens hoped for. As a result, there were big political changes that happened because any time it's the wealthy running things for their own interest, they stirup a lot of resentment amongst those who don't have that same level of wealth.
In an authoritarian regime, the government's power is concentrated in an elite group that has no constitutional obligation to the people. We see this in situations like China under Mao Zedong, where the government power was with this elite group that had gained power through their leadership role in the Communist Party, and then they carried out a series of policies that are really designed just to help them, and again, not promote the greater good of the Chinese people.
The problem with government ruled by a few is that they're not very responsive to the people as elected governments. Again, similar to rule by one, there's no constitutional check. There's nothing that people can do to remove that small group from power. Therefore, again, people become very frustrated in these situations and feel that overthrow or revolution is their only way to get any kind of governmental change.
The advantage of government rule by a few is that, again, these smaller groups can take action quickly and decisively. They can set policy much more easily than in systems where you have to build a broader consensus and consult more different varied groups.