I had a customer once who would just absolutely berate people over email for the tiniest thing. Totally unbearable and unreasonable. So, whenever he would go off, I'd tell him 'look, I'll be in the area [this afternoon|later|whenever]. You going to be around if I stop by?' Any conversation with him that could be deflected to an in-person discussion could be peacefully resolved in short order. Trying to convince him of anything over phone or email was an exercise in frustration control.

I heard somebody say at a conference one time, talking about how much more productive in-person meetings are in reaching agreement, "there's a lot of bandwidth in a room". I think there's a lot of truth to that.

0 - ironically, this was at a ISP network engineering conference