An interface is subjective, not objective. To you the animation is unneeded. But in fact the animations give usability hints. E.g. if you put your mouse in the corner it highlights via the animations that the mouse triggered a hot corner.
Saying such an animation is objectively not needed: it was done as a usability hint. Basically to guide the user. I don't see how you can state that such a hint is not at least in part subjective.
Technically you are right: animations are not needed. But a user interface is more than implementing technology.