Some would express that the size of a target on a computer screen can be considered infinitely large if the button or link is touching an edge of the screen or one of the mouse pointer's boundaries. In such a case, the user may easily move their cursor toward the desired link, overshoot the input to their hearts' content, and still click the link without trouble. This makes for easy access to links with less time spent on aiming.
Luna, the Windows XP GUI, is likely the first instance of Windows to consistently adhere to this design principle in its taskbars. I, for one, find it effective and useful.