Survival Shooter - 07 Harming Enemies - Why we need animation event

I do not understand why we need animation event in Enemy Death Animation and why we need "Start Sinking" function in Enemy Health class as well as the code in Update() :
if(isSinking)
{
// ... move the enemy down by the sinkSpeed per second.
transform.Translate (-Vector3.up * sinkSpeed * Time.deltaTime);
}

If we need this, why we do not need to write such thing in Player's Health and in Player Death Animation?
Thanks!

 

hmmm what?