In the Read node the timing of a node can be changed. It can be shifted forwards and back in time, and shortened at either end.
The TimeClip offers this ability at any point in the node graph plus also the ability to apply fades to the ends of the clip. It is truly a powerful and flexible node.
To learn more about it, and to get the feel for it, I recomend that you study it's functionality in the Dope Sheet. Simply feed it a clip, attach a TimeClip node to it, with its properties in view, fiddle with its Various parameters then study its effect in the Dope Sheet.