Body language is the most obvious. You don't even need very expressive avatars before certain things we naturally do in person become useful tells. I've had multiple conversations in VR, they flow much more naturally than video chats based on the sense of presence.
The quest pro just added expression tracking as well so now you have body language and normal emotional expressions. Wayyyyyyy more natural feeling than video chats, even if I'm seeing an avatar of someone and not their actual face.