Allows you to re-size the Item Preview window by dragging its bottom right corner.
Note: For those that don't know, CTRL-CLICKing an item (in your backpack, bank, chat links, etc.) will display the Item Preview window (also called Equipment Preview).
And for things you can't ctrl-click, here's a game macro you can use to put anything you target into the preview window:
/script ItemPreviewFrame:Show(); ItemPreviewFrame:SetSize(260*2, 350*2); ItemPreviewFrameModel:SetUnit("target", 1)