Live Preview allows to navigate in video by small window when you seek in video by moving mouse on timeline. This is how it looks:
Live Preview window size you can set in preferences or by scrolling with pressed right mouse button.
Besides, you can precisely move mouse cursor and live preview window for desired video frame by using mouse scroll and pressed Alt, Ctrl or Shift. Alt, Ctrl or Shift in this case allows you to control how much to seek.
You can found them in Preferences \ Mouse \ Live Preview tab:
Live Preview required some additional CPU/GPU resources. So we give you mixed option of using it: "when mouse over timeline (on / off with mouse wheel click)". This setting allow you to enable/disable Live Preview on mouse wheel click (with subsequent file reloading). When it disabled, no any CPU/GPU resources spended on Live Preview, when enabled - Live Preview working on mouse over.