With the old/original firmware on the drive, the drive would sleep too aggressively and not wake up in a timely fashion, resulting in the drive no longer found after sleep and requiring a reboot.
Updated firmware has addressed this issue.
However, these drives have shipped with the updated firmware for quite some time now (6 months? A year?) so although updating drive firmware is usually a good idea, if your drive is new it probably already has the new firmware.