The Enable computer and user accounts to be trusted for delegation user right must only be assigned to the Administrators group on domain controllers.
Inappropriate granting of user rights can provide system, administrative, and other high-level capabilities.
The "Enable computer and user accounts to be trusted for delegation" user right allows the "Trusted for Delegation" setting to be changed. This could allow unauthorized users to impersonate other users.
How this relates to the STIG checklist: STIG vs SCAP benchmark.