For VoLTE, besides better voice call quality (which may however not be too noticeable), it can do full 4G speed data transmission during the voice calls. Without VoLTE, 4G will go down to 3G during a call. Thus data transmission will be slow. Imagine when you are on a call (using a hands-free, wired or BT), you can with VoLTE still work on emails at normal full speed, download or send large attachments, hop over various websites, work on the files at your cloud drives, etc, etc. This is extremely useful for those who need to frequently attend long conference calls when they are on the road....