The lead sheet is the backbone of contemporary music. However, not all chord symbols are created equal. The notation of extensions (sharp 11s, flat 9s), alterations, and slash chords requires precision. A will standardize these symbols. For instance, is it better to write "C-7" or "Cm7"? How do you notate a specific bass motion under a static chord? Berklee standards provide a uniformity that jazz and pop musicians recognize instantly, reducing the cognitive load on the rhythm section.
Perhaps the most valuable section of any notation text is the transition from score to parts. This is where amateur copyists fail and professional engravers succeed. Berklee resources provide checklists for part preparation: Berklee Contemporary Music Notation Pdf