Then what's the point of the jury? To be redundant? I mean if the guy clearly had an illegal amount on him then under that line of thinking he will serve a punishment so there's no need for a trial.
To answer your question, officially, a jury basically has two and only two jobs:
1. To weigh the evidence and decide the facts. This is the jury's and only the jury's job. The jury and only the jury decides what they believe actually happens after hearing all the evidence. In this case, yes, there probably isn't much for this particular jury to have decided. Was the guy actually in possession? I suspect there will not be much dispute. And I also suspect that there will not be any applicable defenses where they will have to decide whether any facts are true that would serve as the basis for a defense. But a lot of cases are not so clear cut, so the jury's role in this regard is more difficult and the necessity of having an impartial jury decide the facts is probably more readily apparent.
2. Applying the facts to the law. This part of the process is supposed to be almost entirely mechanical. Once the jury decides what actually happened, they are to apply those facts to the law as stated in the jury instructions and then render their verdict accordingly. During jury selection (which is apparently the stage in the process at issue in this case), jurors are to state whether or not they feel they actually
can carry out that duty regardless of any personal bias they may have relating to either the parties or the law at issue in a particular case. If they say they can't, the judge is supposed to excuse them. If their answers to questions may simply
imply that they can't or might not, it is up to the attorneys on either side to excuse them. Simply put, it is a juror's duty and responsibility to follow the law, whether the juror subjectively supports that law or not. That being said, the system is set up in such a way that a juror who feels as a matter of conscience (or for other reasons) that he or she cannot do so, he or she is to be excused without punishment or retaliation. Unfortunately, that simply gives an easy out for people to cop out and say they can't do their duty if it conflicts with whatever pet cause of the day strikes their fancy. But for better or worse, that's how the system works.