Yah MTBF is high but any amount I can help save my drives is good for me.

If I remember right, it's more stressful on a drive to spin up and down then it is to stay spinning for a long period of time. Most of the Y2K "problems" were caused by companies shutting down ancient hard drives (the tower sized ones that probably stored a few hundred megs at best) then trying to get them to spin back up. MTBFs are so high anymore that either is not really a concern. But again, spinning them down and up will probably shorten that time.