California Code, Penal Code - PEN § 1054

(a) To promote the ascertainment of truth in trials by requiring timely pretrial discovery.

(b) To save court time by requiring that discovery be conducted informally between and among the parties before judicial enforcement is requested.

(c) To save court time in trial and avoid the necessity for frequent interruptions and postponements.

(d) To protect victims and witnesses from danger, harassment, and undue delay of the proceedings.

(e) To provide that no discovery shall occur in criminal cases except as provided by this chapter, other express statutory provisions, or as mandated by the Constitution of the United States.