They determine if there is enough probable cause to warrant a trial
Explanation:
The purpose of a preliminary hearing is to determine whether the prosecutor has enough evidence to justify further criminal proceedings against the accused.
At a preliminary hearing, a judge hears the state's evidence and decides whether there is sufficient evidence to require the defendant to stand trial. ... No judge is present but the grand jury is instructed to review the evidence according to a probable cause standard and determine whether there is sufficient evidence.
