What is ginger used for when served with sushi?

Why do sushi restaurants give you ginger on the side? I've seen people mix it in with their soy sauce/wasabi dip (which I think is kind of strange) and I've also heard people say that it cleans your pallet... what does that even mean if it's true

Cleaning your pallet is simply taking the taste of a food out of your mouth so it is ready for a different taste. When you eat sushi, you tend to eat more than one flavor.When you eat a small piece of ginger in between different types you get the best flavor of the sushi.