I always validate my drives before putting them into my 'production' use because I don’t like surprises down the line: most hard drives are shipped without the media being tested. Moreover, a good hard drop off the delivery truck can damage a drive.
Recently MPG purchased five Hitachi 7K4000 hard drives as test drives (as shown, 6th drive was a replacement for one bad one). It was especially important that they perform similarly becuase they might be tested together in RAID-0, RAID-1 and RAID-5 configurations. To have one slow drive slowing down the others would be an issue in general, and particularly so for testing accurately.