Countries all over the world use some form of a jury system, presumably because they have not found a better way to consistently ensure that defendants receive the fairest possible trial; however, that does not mean the system is without flaws. There are both advantages and disadvantages to a jury system.
The advantages of a jury system include the fact that the public generally accepts jury verdicts, and lay people, their "peers," are more trusted, often, than judges. A jury is, in theory, unbiased because it is not part of the justice system, and jurors are allowed to apply common sense and local values to the evidence and facts of the case. It is an efficient system, more than eight hundred years old, and it provides citizens the opportunity to actually be involved in their communities.
The disadvantages of a jury system include the vetting process, which precludes the random selection of peers, and the inability to assess jury bias after the verdict has been determined. Jurors are human and they make mistakes; even worse, jurors might come to a hasty verdict to suit their own desires to be finished with a case (especially in very long trials). Jurors might also be easily influenced by presentation and showmanship over substance, and they are not likely to have a complete understanding of every point of law raised in the case.
It is clear that there are risks to having a jury trial; however, it is part of a system of justice, at least in America, which has generally worked and will undoubtedly continue to be the law of the land.
For a more extensive list of advantages and disadvantages, refer to the link sixthformlaw link below.