What is the effect of a grand jury deciding to suspend action on a witness who has been granted immunity?

"A grand jury ordinarily deals with many inquiries and cases at one time, and it can rather easily suspend action on any one, and turn to another . . . . Trial courts, on the contrary, cannot be expected to dart from case to case on their calendars anytime a witness who has been granted immunity decides not to answer questions. In a trial, the court, the parties, witnesses and jurors are assembled in the expectation that it will proceed as scheduled." United States v. Wilson, 421 U.S. 309, 318, 95 S.Ct. 1802, 1807, 44 L.Ed.2d 186 (1975).