Snaps the time slider to the cursor position. When on, clicking the cursor in the Track View window moves the time slider to that spot in time. When you release the mouse button, the time slider jumps back to its previous position.
Turning on Sync Cursor Time also turns on so you can edit keys anywhere in Track View by dragging them and see your results right away. The time slider jumps to the frame at which the key resides and the viewport displays your changes in real time.