Some hardware raid controllers do that with their battery backed cache - they return written before it’s flushed to disk because they have a battery in case of power interruption.
On power loss the drives will immediately lose power, they have little capacitors in them that allow the head to safely rest on power loss. (it used to be that the head just crashed into the spinning platter, can you even imagine).
Part of the Server boot-up is to flush the raid caches, which are battery backed volatile storage. (and the batteries are fairly big so can last about 7 days in most cases).
The battery being big doesn't matter to the drives though, there would be no guarantee that you could finish writing the cache to the drives with the capacity of the battery: since drives use a considerably larger amount of power than keeping some DIMMs hot.
I remember as a kid running PARK.COM to park the heads before powering off the computer every night; I continued this habit for many years after I got my own computer, until I learned that hard drives now have mechanisms that make this unnecessary.
If I remember correctly, it was not that bad. The head being parked in a random place meant it could damage the plate if the disk was moved or shaken. I think that modern disks would indeed crash (if not for autoparking) but they have much smaller flying heights and thus require serious active magic to keep the head from hitting the plate.
Parking would mean you could move the drive and the head wouldn't bounce off the platter.