position.Set vs. position = new Vector3()

Why does vector = new Vector3(..) work, but vector.Set(..) does not? The Documentation of Vector3.Set does not list any special cases.

Detail:

I want a gameobject to follow the cursor. Therefore I call in the Update method the function stickItemToCursor() that will achieve this.

This works:

 _itemInUse.transform.position = new Vector3(mousePosition.x, mousePosition.y,  1.0F);

... but Vector3.Set(..) does not to work (the position does not change):

 _itemInUse.transform.position = new Vector3(mousePosition.x, mousePosition.y,  1.0F);

Edit:

Solution: transform.position is a getter - so it returns a copy of the Vector3 where the position is stored. If you call Set on gameObject.transform.position only the copy will be edited.

Discussed here: http://answers.unity3d.com/questions/225729/gameobject-positionset-not-working.html