I don't exactly know what it is used for. Can someone explain it to me and what advantages it has to the Phantom 3?

The lightbridge can work with our DJI flight controller A2, WooKong-M, Naza-M V2, Phantom 2, while Phantom 3 has the built in video downlink, for more details, please refer to our DJI official website to check
http://www.dji.com/cn/product/dji-lightbridge/feature

DJI-Cathy Posted at 2015-9-10 04:50
The lightbridge can work with our DJI flight controller A2, WooKong-M, Naza-M V2, Phantom 2, while P ...

Thanks. You just answered all my questions.