The system is used to interrogate the proper and fair would be found if one partner is in a competitive State. For example, in case of disputes between people, or private, State, etc.
Using trial would be appropriate and fair to one party in a disadvantageous position. Such as disputes between private citizens or the state and so on.
The use of the inquisitorial system is reasonable and fair to the party, one is in a state of disadvantage. Such disputes among the people, or between the government and private sector.