That's a broad question that could be approached a number of ways. Essentially, with a jury, you are taking sometimes complicated legal issues and placing them in the hands of laymen who are more likely to be motivated by emotion than reason, so one "impact" is that it can sometimes limit or remove legal justice from the courtroom equation and replace or supplement it with a human factor. Now there have to be attorneys who specialize in jury selection, as many have argued that is where a case is truly won or lost.
Another more significant long-range impact is the additional cost the justice system and individuals have to bear in order for us to conduct full jury trials, as well as the extended amounts of time involved to do so as justly as possible. This delays other cases, sometimes for years, can cause changes in venue, mistrials and opens up the possibility of jury tampering and misconduct. In short, it makes the practice of law and the administration of justice much more complicated.