It’s for more throughput … effectively it’s got 3 antennae built in, one vertical and two horizontal. AP device with 3 TX/RX chains is needed to take full advantage. It’s not completely necessary that the other end is triple-chain as well, the link can benefit by employing Tx and Rx diversity on one end only.
GPS utilizes 1.57GHz (and 1.2GHz), GLONASS utilizes 1.6GHz, Gallileo 1.6GHz (and 1.2GHz), BeiDou as well … None can be effectively received using antenna for WiFi (either 2.4GHz or 5GHz).