The `smartmontools` drive database can be seen here. Its purpose is to provide additional command-line flags to both `smartctl` and `smartd` for drives where the default settings (which are themselves defined in the database) aren’t sufficient, and/or to provide warnings about the drive.
Many drives have specific counters, or counters that need to be interpreted in specific ways; see for example the first non-default entry in the database.
Some drives have important misfeatures which users should be told about; see for example m4 SSDs with their counter bug.
USB drives need an access method to be specified, see the entries starting here.
The database isn’t _needed_ , since all the settings it defines can be specified using command-line parameters; having it saves each user from having to determine those command-line parameters themselves.