Hard disks attached to the system as an ordinary mass storage device tend to disappear completely from the bus in case a bad sector has been hit. Learned about this while building RAID over USB at one of my former employers (don't ask). While SAT is virtually a passthrough over USB avoiding such disappearances and its presence is mandatory in, for example, data recovery scenarios.

Before(?) SAT, there was Cypress' ATACB for the same purpose: https://www.cypress.com/documentation/datasheets/cy7c68300c-...