Because it forces the guitarist to think vertically. In the section regarding the "II-V-I" progression, Vincent demonstrates how to connect these voicings with minimal hand movement. He teaches the concept of —the art of moving from one chord to the next by shifting only the notes that need to change.
This 69-70 page spiral-bound book is considered an essential guide for guitarists looking to emulate the lush, "block-chord" sound of legends like Wes Montgomery and George Benson. Jazz Guitar Voicings Randy Vincent Pdf 51