Sheridan or Sherman, or any of the others, the practise was the same. The "Unofficial Policy" was to punish the South for "starting the War" under the cover of fighting a war. That attitude was encouraged an "anything goes" policy as to the destruction of private property in the south, that had nothing to do with any Military objective.

Most of Lee provisions by 1864 was not coming from the Valley, but from North Carolina. So destruction of the valley had nothing to do with defeating Lee's Army at Richmond, other that to draw off Early's command from Richmond to counter Sheridan in the Valley.

And even then Early marched all the way to the outskirts of Washington anyway. So what good was Sheridan doing in the Valley?