What does the Fillet & Chamfer option do in the Acad 2K5 Extended Offset express tool?

Greetings:
Could someone please explain what is the Fillet & Chamfer option (Express TB - Modify - Extended Offset - Enter Distance - Options -
Gaptype...) does in the Extended Offset Express tool? I try both and don't see any difference for the object (Rectangle, Square, Step Polyline etc.) that I want to offset.
Advance thanks for your time and helps.
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