You cannot use that randomness for private key or private data generation, true. But there are less common usage scenarios that need unpredictable randomness th

You cannot use that randomness for private key or private data generation, true. But there are less common usage scenarios that need unpredictable randomness that is guaranteed to be generated only after a certain point in time. For two party protocols you can exchange nonces to prove that both parties are participating in this exact moment, but those don't scale to thousands of mutually distrustful parties. An example for that is the proposed Bitcoin protocol change that is already cited by swordswinger12 which prevents attackers from hoarding Bitcoin blocks.