Dubin's "Rapid Interpretation of EKG's" briefly describes this part of human physiology but doesn't explain the reason behind it.
Is there a specific advantage of the human heart having this characteristic, or is it a flaw/useless trait?
Why is a philosophical question, but you can see, below, the most common anatomic variation, with the ventricular septum receiving terminal branches from the septal fascicle off of the left bundle branch though it can come off the common bundle. The left ventricle is larger, and as might be expected, has a greater portion of the conducting system than the right ventricle.