It's a psychological thing, I figure. If they see your face, it gives a better sense of familiarity. You know this person, you know they are there, so if something happens, you got another person on your list. Can't do that with a text message or a voice, unless you're good at tracing it back to the source or listening.

Me? I just want to know who I would say hi to if I bump into you on the road.