And the prize goes to AOTW.
From my memory (which is generally suspect!!):
There is a very in depth explanation of the reason you do this, all related to 3 D cams and what not. To simplify the explanation, the FCU governor has some "computer" functions, which are nearly all hydro mechanical. When in the governed mode, you will not feel the bleed band open and close, but when selecting Emergency Governor, you have deselected the "computer" functions yet the bleed band remains operating. Thus when you get to higher power settings during landing, the closing and opening of the bleed band is not damped out by the computing functions and is felt as engine/RRPM surges that more often than not cause pilot to over control during the landing phase of emergency governor, though not really unsafe for the average pilot. Another reason to perform a shallow and slow running landing.
By beeping the N2 governor to it's lowest limits, you are mechanically tricking the bleed band into inaction by moving the N2 governor actuator far enough that through the magic of smoke, mirrors, and 3D cams, the bleed band actuator is not stimulated by the higher power settings. Thus termination to the hover can be made without engine surge in Emergency Governor.
I will seek a better explanation in the next week or so if you are still intrested.