Jury duty can be a pain that no one wants to do, but if all verdicts and sentences were just decided by judges or government officials, the government's power would grow and we would all be at risk. The right to have a jury trial keeps the nation founded on the principle of everyone being involved in government, so yes, juries are beneficial.
I do think the use of juries is beneficial to the United States Justice System. It is much better than leaving all of the power in the hands of a judge or magistrate. But I do think there should be professional jurors for cases. People who go to school just to be jurors.
Taking every case to the extent of the law doesn't always work. Sometimes it does help to have a set of people weigh the options and make the ultimate decision. While the jurors may not be the most expert advisers in the situation, they will share more opinions than a single judge. They debate the issues between themselves and come to the best decision they can. Appealing to human compassion can help people avoid unnecessarily hard punishments.
I don't like the use of juries in the US Justice System. I understand the reasoning behind it but don't think it is right. You are pulling people who know nothing about the law or crimes being committed and asking them to decide the fate of an individual. I think there is a serious flaw there.