Ammeter bypass

It gets rid of the ammeter in the circuit, which itself is a known weakness in the system. And it bypasses the bulkhead connector, which isn't a good way to run that kind of amperage. Which is why you can often find burned or melted terminals at the bulkhead.

As far as increasing battery voltage, it shouldn't. Or at least not much. You probably eliminate some losses by getting rid of the less than great bulkhead connection, but that's minor. The real benefit is from eliminating the ammeter, which can kill the charge circuit and can cause fires, and the high amperage connection at the bulkhead, which can cause fires as well. It's a more of a safety and reliability improvement than an efficiency improvement.