I have a dedicated apple mac mini and 4 external 4TB drives. I do not leave them on when not in use. I use one drive as the main library, the second as a back up that runs every month, third is all my hi rez music for music player and the 4th drive for a back up to the hi rez drive. I leave the two drives plug in by usb and plug the other ones in when doing a monthly back up. Could I leave them on all the time, sure, just trying to save life expectancy. JP