I never really thought about it that much, but now that you mention it, I use to ride my 1975 GoldWing one-handed lots of times. On long cruises I would keep "snacks" in the faux gas tank glove compartment and that was the only way to get to em on the road.
One hand on the handle bar is the best way to show somebody that you're actually turning the handlebars in the "opposite" direction when you make a turn at speed too. (Lots of people don't believe it when you tell them, until you prove it).