It has following Advantages over LTE
1: It has improved voice quality. Usually voice networks transmit 08 kbps codec but VOLTE works between 13-15kbps codec. It allows more clarity on voice call.
2: It uses HD video services and offers high quality of video calling rather then traditional video call.
3: Call setup time is very less. Means you will not hear beep beep sound while connecting your call. But its only possible when both users have VOLTE network.
4: If you are using VOLTE then you can call and use network data at the same time. It means you can call your friends and browse Google services at a same time.
5: VOLTE didn't charge for sending messages on watsapp as mobile data. So its cheaper then Watsapp and Viber.