Assuming market fluctuations are random, this will cause markets to ratchet up.
This is such an obvious scam.(http://www.autoadmit.com/thread.php?thread_id=3863191&forum_id=2#35179543)
But why not allow you to cash out all at once? I also heard these exchanges engage in fractional reserve lending.(http://www.autoadmit.com/thread.php?thread_id=3863191&forum_id=2#35179573)