In case of AP350 , two antennas ( right and left ) are for DIVERSITY purpose .
In the indoor enviornment there are too many multipath reflection which can cause too many retransmit and can reduce throughput .
You can use TWO antenna on a same AP to cover DIFFERENT Coverage area as when one antenna is listening other is deaf .
Both antenna should cover same coverage area and it is used for diversity reason only .
so in summary you can have one antenna but diversity is disable and if you have two antenna then you are taking advantage of diversity