This harness connects two battery packs in Series.

For example, you can make 2 x 2200mAh 11.1v 3S1P packs into a single 2200mAh 22.2v 6S1P pack.

Its an excellent and cheap way of buying larger lipos.
It also means that if you have a crash and damage a cell the loss is far less than losing an entire 6S1P pack.

Its the smarter way to run larger packs.