In any court or regulatory tribunal there are a minimum of three participants.
First, the party seeking an order. This the prosecutor in a criminal or regulatory matters or the plaintiff or applicant in a civil or family case.
Second, the party seeking to avoid an order. This is the defendant or accused in a criminal or regulatory matter or the defendant or respondent in a civil or family matter.
Finally the party who decides whether to make an order. This is the judge, justice of the peace or tribunal.
Often the parties are made up of more than one person. So judge is sometimes a judge with a jury and tribunals are usually made of more than one person. The accused in a criminal case can be several people (say two people accused of robbing a convenience store) and the plaintiff in a civil case can actually be many different people (think of the plaintiffs in the Residential Schools cases).
Regardless of how many people are involved, the roles of the parties seeking an order and the parties trying to avoid an order are, by definition, partisan. Each of the parties want something and so they will argue as strongly as they can to get it.
The party deciding whether to grant the order or not, by contrast, is not looking for anything and is impartial. A judge doesn’t care who “wins” a case so long as justice is done. A plaintiff who loses a lawsuit doesn’t get any money – a judge who rules against that plaintiff gets the same salary regardless of the outcome.