This connector is designed to connect 2 lipo batteries in series doubling the voltage of the battery. Capacity will remain the same.
For example 2*1800 mAh 11.1V batteries connecting using this would become a 1800mAh 22.2 V battery.
Advantages include: Cheaper way to acquire large lipos, if you crash and damage one battery the loss is not so great and people tend to have more smaller batteries lying around that they can utilise rather than spending more money on a bigger battery. *Combos of these leads can produce fantastic combinations of voltage and capacity and you have the room to position on the helicopter due to long wires.