Why Travel?
People take backpacking trips at any point in their lives. It is especially common for younger people in their late teens / early 20's, as people at this age generally have fewer ties like mortgages, children or an established career.
"Gap Year" is often used to refer to students taking a year out prior to starting university or after graduating before settling down into the world of work. For others it may just be the desire to escape the rat race, after all you have the rest of your life to sit behind a desk!
Whenever you take a backpacking trip, hopefully the reason will be the same. You want to broaden your horizons, see new cultures, see new places and meet different people.
It is often reported in the media of the benefit that companies and universities gain from a candidate who has taken time-out. Time spent teaching English to children in Peru make your CV stand-out, hinting that the experience may have made you a more rounded individual.