If you have a multihead display, with multiple display/screens instead of one giant virtual screen, this program is useful. To use it, you should bind it to some key sequence in your window manager. The program allows you to warp the pointer to a different screen, so you can move the mouse easily between monitors with just a single keystroke (keeping the same X and Y positions).
Xwarppointer also allows you to retrieve the current position of the X cursor, so you can build more complex logic to move the cursor using a scripting language wrapper such as Tcl or Perl.