The standard reference for "pointer warping" for Tk has been the "usage FAQ" [L1 ]. It briefly mentions that pointer warping is a bad idea, supplies source for an extension which implements warping, and also points to [fill in the details here ...], with its implementation of the same as ... The FAQ doesn't seem to be current ...
As "Changes in Tcl/Tk 8.3" hints, release 8.3's event command builds in pointer warping.
Here is a simple example of pointer warping:
event generate . <Motion> -warp 1 -x 50 -y 50.
(Move the cursor to the '.' window, inset 50 pixels from top left corner)
Among the legitimate uses of pointer warping are test automations, including Android, and for pedagogic purposes (Android can also help build demonstrations).