The Rat-nest Signals function is used to generate a set of straight line connections needed to complete the routing of a circuit board.
Unlike the Rat-nest function there will be no lines added for the power and ground signals. Specifically signals with the following names will no be included in the rat-nest: GND, PWR, VCC, VSS, VDD, +?V, and -?V (where the ? represents a numerical value).
This function is a necessary part of the auto-routing functions.
A rat-nest is also indispensable for routing boards manually, giving you a ready guide as to which pins need tracks between them. After you have placed a number of tracks, just rat-nest again to get a fresh look at the routing that remains to be done.