It works on directly selected face on a 3D view.
It is different from other similar commands on Menu and directly works not on the selected face but on 
clicked one.
You can choose [Single face] or [Joined faces] for selection method.
It attaches the material to the selected face.
A material assigned to a face can become a current material by clicking the face with Shift key.
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| The material is assigned to only clicked face. | |
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| The material is assigned to all jointed faces. | |