Majority of the reasoning deals with wire lengths vs. power draw. Most people decide to do a big 3 because their lights dim. So they go down a tumultuous path of upgrading wire anywhere and everywhere.
Most don't realize that their current grounds are either old and rusty or never maintained enough surface area with the grounding point in order to be effective.
So...you can only draw as much power from the positive as your ground is able to theoretically dissipate. If your grounds are not connected very well then you aren't going to be able to draw much power.
