The credentials plugin version 1.21 added the possibility for allowing the user to specify the ID of newly created credentials (issue JENKINS-26099).

Release notes for creditentials plugins states:
"Credentials defined in other plugins need to use BaseStandardCredentialsDescriptor to pick up this feature"

Finding credentials by description in the Job-DSL plugin (version 1.30) has been deprecated.
So this functionality is needed when using the Job-DSL with ssh credentials.