I should think that it isn't relevant to digital copying at all, but 
back in the analog '70s we used to high speed dub reel to reel tapes 
backwards because seeing a decay as a transient was much easier on 
the electronics than an attack, especially a percussive one.  That 
was the recommendation of Ampex, who built our duplicators.

Bob Cham

>Back in the day when duplicating tapes was a day job for me, they 
>said that side 2 of cassettes duped ay high speed both sides at once 
>would sound better than the side 1 would. Never made much difference 
>on cassettes, especially at 64 or 128IPS dupe speed, but some people 
>told me copying 2 tracks worked better in reverse too... They said 
>the electronics could respond to transients backwardsbetter than 
>forwards. I have no empiric evidence of this though.
>
>Just old tape tales by now, but this had me thinking back... or backwards!
>
>I have transferred some quarter track tapes doing all four tracks at 
>once top a four channel A/D, and not noticed a significant 
>difference, but it is easier to do them one side at a time as then 
>they end up tails out, as long as it is an hourly job and not a mass 
>flat fee transfer project.
>
>Hope this isn't irrelevant!
>
>Lou
>Lou Judson
>Intuitive Audio
>415-883-2689
>
>On Oct 8, 2009, at 1:59 PM, Richard L. Hess wrote:
>
>>
>>>It's not the digital realm, its the way the reel electronics 
>>>handle transients and phase
>>
>>There appears to be waveform differences between playback in the 
>>two directions after accounting for the polarity flip. To my ears, 
>>this is an acceptable tradeoff for copying oral history tapes in 
>>half the time. This is especially true of mid-to-low-fi recordings 
>>such as some 3.75 and most 1.88 in/s reels.
>>
>>Cheers,
>>
>>Richard