Cats tongues are natural grooming tools, they are pretty effective for short haired cats. Although the downside is that they swallow hair which forms hair balls and makes them vomit! Occassionally however they will block with hair balls and need costly surgery.
Fortunately cats usually love to have their owners groom them, its just one more little service we can provide! It helps create a bond with cats which naturally indulge in mutual grooming, it is best started with kittens.