I've found that spindowns on slow enough drives can cause an ATA error to pop up in dmesg, followed by it marking the drive as 'dead' and vanishing from the system until rescanned with scsi commands or reseated in hte host for redetection.

For that reason, I have them always spin.

As for anyone who doesn't have that specific issue (Drives which take forever to spin up from sleep) you still never want to have them spinning up<>down day in and day out as it'll ware out the motor who has to give its all just to spin up.

It's much easier on the internal hardware to just let it spin indefinitely instead of the heavy lifting involved going from 0RPM > 5400RPM (or 7200RPM) multiple times a day.

Don't even try to argue "But what about x per day, month, year" they're still recurring spinups based on idle time, drives hate that shit.