I'd say, one of the main reasons is - fun! It's fun to check out other places, it's fun to get away from all responsibilities of home for a while, it is fun to eat different things, see different things, learn and expand.
What I do is mainly dependent on how I go, if together with others or alone. When I'm alone I love to be on my way, check out new places every day, scoop out new shops and little towns and nice landscapes. If I go with a partner, having a place to hang out would be more important, staying a few days, relaxing together, have enough time to enjoy intimacy and the relationship in the first place. If I go with a group, mostly it would be a group setting anyway, either a seminar or a cruise or so, so the schedule would be less flexible.