Please explain the logic of this. Surely your footage won't become sharper, right?
Slightly! It does. I don't really know why. But when I was running my first raw tests I tried both exporting 1600x800 tiff than opening in QuickTime 7 and exporting 1080p with letterbox and exporting an 3k plus tiff and downscaling to 1080 p with letterbox. The latter gives me better results.
My guess is ACR handles upscaling better than QuickTime, and any video conversion software will handle downscaling better than upscaling.
Does this make any sense to anyone else?