http://www.pehub.com/146588/the-%E2%80%9Cfacebook-problem%E2...
The second argument I've heard is that it allowed Zuckerberg and some of his closer companions to cash out a large chunk of cash for the first time.
Facebook itself did not need money to my knowledge
http://www.pehub.com/146588/the-%E2%80%9Cfacebook-problem%E2...