It can hold a mirror up to our society, and help us to better understand how and why we do the things we do.
Without that knowledge of other cultures, there are many things we do that we don't even question - don't even really realize we're doing them, just because that's the way we've always done them.
Some of them are pretty fundamental things that no one ever really thinks about - like why do we generally eat three meals a day? Why do we typically eat sweet foods as snacks and rarely share, but meat meals we usually gather together as a family, and share? Why do we tend to prefer well mown lawns with a few trees on them - and if possible, with a view of water?
Why do we tend to work and go to school from morning until afternoon? Why not start at noon and go through the evening? Why do women generally wear make-up and dresses, while men have short hair and wear pants? Why do we eat shrimp and lobster, but avoid insects?
No one even questions these things, or how universal they are until they start looking at other cultures that may not share those same traits - and suddenly realizing that there may be different ways of doing things, and different ways of viewing the universe.