A preliminary hearing can be about a number of things and there can be more than one. For one, Preliminary hearings give the defense an opportunity to discover what the prosecution has on the defendant and can actually be conducted as a mini-trial with witnesses and evidence. It can also result in a judge's decision to reduce or eliminate charges. Plea deals are with the prosecution, but must be approved by the court.
Because of the low burden of proof needed to hold a case over for court in a preliminary hearing in PA, seldom are charges dismissed at that level, but it is an excellent discovery tool and offers a basis on which to impeach the testimony of a witness in trial.
