Efficiency: the government may be more efficient because a few people take all the decisions, with barely or any opposition, which can make any process run faster.
Order: the government can more easily impart order in society because its authority is unopposed. This can reduce crime, and improve public safety.
Disadvatanges:
Authoritarianism: a government concentrated in a few hands can become very authoritarian, to the point of violating the human rights of those who oppose it.
Totalitarianism: this type of government can become so authoritarian that it turns into a totalitarian government: one that controls every aspect of its citizens: from the people they vote for, to the way they dress.
Corruption: a government without opposition, concentrated in a few hands, can easily become corrupt, and reduce the welfare of its citizens because of that.
The First Amendment to the U.S. Constitution guarantees the right to freedom of speech, but that doesn't mean that people won't be offended by your words...
