The motivation behind this layout is accessibility. The goal is to provide a way to see all abilities, hot keys, cool downs, and utilities all in one centralized place.
This theme aims to be concise and clear: All the information you may need/want, all in one place, so that you don't have to always be searching your ability bars and can actually "look up".
The left side quickslots allow for a logical key-binding assignment, from lower row upward, so that "eye-finger-coordination" is pleased.
The right side quick-slot bars allow for quick mouse clicks to abilities you don't have bound, as well as a useful place for utility/out of combat abilities.
Under the left character portrait is the Focus target frame, and underneath the target portrait is the target-of-target frame.