This is especially useful for Tablet PCs, UMPCs and Touchscreens, where you do not use your mouse (normal computer, with mouse can also use).
It provides PDF readers style grab and drag page scrolling and scrollbar-style scrolling initiated by dragging anywhere on the screen.
Grabanddrag can recognizes mouse Flick gestures for scrolling up, down, left, or right a screen at a time, handy for pen based computers.
It also supports page Momentum. If you enabled, when you releasing a page you have been dragging at a constant velocity will cause the page to continue moving at its current speed until clicked to stop.