In portal what does the companion cube do

The Companion Cube is the same thing as a normal weighted storage cube, with the minor difference being that it has a heart painted on it. In one level of Portal, GLADos (yes, it's spelt like that) gives you the companion cube with the intention of finding out how you (the test subject) deal with loss. She finishes that test chamber by asking the player to euthanize the cube, locking the elevator until the cube is dropped into a pit which GLADos calls the 'Aperture Science Emergency Intelligience Incinerator' After the 'death' of the cube, she often reminds you that you 'killed' it. (Something akin to 'we were going to have a party for you, all your friends were invited, too bad you don't have any friends because you killed them') Appearently aggravated by this, Chell proceeds to pull the hapless robot apart and throw the pieces in to a burner.