I'd say traveling abroad gives context to learning new things. Reading literature set in foreign lands can give you an idea about a place, but until you've been there it's really difficult to understand the places and people being discussed.
Also, living in one place for all your life and never leaving can make you forget that places outside your own exist. It can be hard to create a frame for thinking about global events. Traveling helps you to remember that America is not the only country in the world, and that life is vastly different for people in other places.
The final reason I'd give is FOOD! :)