The overuse of email as an alternative to a call creates emotional distance. In advertising, it is said that the medium is the message. In this case, the medium is email and the message is "I don't actually want to talk to you."
When we're unthinkingly throwing "best" at our children or "xo" at a new business contact, we may be missing a crucial leap of imagination: what the person at the other end of the line may be feeling, thinking and expecting.