Excuse me but what does a CFO really do?

What does the CFO do and how will you know you need one?
Is it worthwhile for a young startup that has just raised money to take on a full-time CFO? Should the CFO be an expert in finance or economics so that he or she is also proficient in investing and fundraising?
Check out the answers below by our legendary CEO & financial services leader, Aviad Sorek.