It simply allows a deeper receiving position - the hips can drop beween the legs.
Some of them do get hurt - not a huge number, but it's not unheard of. What you see more often is chronic problems - constant pain, inflammation, etc. There are a lot of lifters at that level who have had multiple surgeries. Last year at the olympic training center, natalie woolfolk was the only resident female who had never had surgery (and now it looks like she needs it on her shoulder). So while you don't necessarily see acute injuries often, you can never predict when you will get one, and you can pretty much count on long term problems.
That said, it's the opinion of some smart people (tommy kono for instance) that training like that will develop connective tissue elasticity and strength, which will prevent injury. Hard to say.