My coverage of edit commands has been, admittedly, sparse, but this new feature in AutoCAD 2012 caught my attention, and my suspicion is it will catch yours as well. Very simple, but very helpful.
I think the most useful circumstance would be in the application of unequal distances when using the Chamfer command.
In the following exercise, you will set unique values for Distance 1 and Distance 2, so consider the drawing size when doing so.
Draw any rectangle, then launch the Chamfer command  and you get the following prompt; enter D for the Distance option…
Select first line or [Undo/Polyline/Distance/Angle/Trim/mEthod/Multiple]: D
Enter a reasonable value (based on your rectangle size) for the first chamfer distance, then enter half that value for the second chamfer distance, similar to that shown here…
Specify first chamfer distance <12.0000>: 10
Specify second chamfer distance <10.0000>: 5
After specifying the distances, select one line of the rectangle, then hover over the adjacent leg of the rectangle to see the preview of the chamfer!
As you see in this example, the preview is very useful in alerting you to a possible reversal in the selection sequence in this circumstance.
See all the articles published in June 2011
See this article in the June 2011 Corner
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