Being able to see what happens when you deviate, reenforces the norms which have been broken, and teaches both the accused and the accusers that there are proper and good ways to deal with criminals. The summary style is concerned mostly with efficiency. It is assumed that most of the cases dealt with are open and shut. There is no need to go into great detail or justifications for what happened. Judges make decisions on the basis of written and oral presentations.
Time is money and cases have to move.
A good example is traffic trials in the United States, which can be requested. In these trials, there will be little questioning of legalities or Constitutional principles. The judge will first ask the police officer what happened, and then ask the accused. Unless there are extraordinary instances of stupidity or abuse by the police, the accused will get to pay the fine or serve the weekend in jail. The standard for judging guilt or innocence is not so much based on the law as on the rules devised by government agencies.