The Load and unload device drivers user right must only be assigned to the Administrators group.
Inappropriate granting of user rights can provide system, administrative, and other high level capabilities.
The "Load and unload device drivers" user right allows device drivers to dynamically be loaded on a system by a user. This could potentially be used to install malicious code by an attacker.
How this relates to the STIG checklist: STIG vs SCAP benchmark.