I just read the news about SATA Rev. 3.3
SATA-IO Expands Supported Features in SATA Revision 3.3 Specification
I don't mention about what's updated here, but I think "power disable" is a good feature.
SATA drive itself supports hot plug, but without any mechanics, you need to pull the drive with the condition "power is still supplying". This should increase the risk of breakage, since when you pull the drive, drive doesn't have the way to control itself, head and still spinning. And possibility to heads touch to the media.
Of course, you could send command to stop the spinning even under current specification. But its purpose is just for power saving. So if system need to access to the drive, system will start spinning of the drive. I can't say it's never occurred during you send this command to HDD then walk in to the place which HDD is used.
I think it's nice update.
To be continued,