Toe changes are primarily caused by four conditions; outer tie rod too low or too high and tie rod length too long or too short. Items like this, and others attached to the link, allow the tie rod ends to be relocated up or down, provided you get the correct style of spacer to mate with the steering arm and tie rod taper. If you have rod end tie rods, this adjustment is even easier with a thru-bolt arrangement. This relocation accomplishes the same thing as heating and bending the steering arm to relocate the outer tie rod pivot point.

Of course for some its easier to simply fire of the hot wrench and tweak a steering arm than it is to sort through a variety of spacers and tapers. If you don't have access to an oxy/acetelyne set up to heat up an arm, spacers are an option.