before CTS, it is assumed the clock is ideal and reaches every single flip flop at the exact same time. In reality, after the CTS, there are small differences between clock arrival time at the nodes of the tree. Sometimes the difference helps you, sometimes it hurts you. Think of it as a timing window that stretches according to the clock arrival time at launch flop and arrival at destination flop.From viewpoint of timing closure, what is different before and after CTS?