In Prisma Cloud, assigning an administrative user to an account group is a way to implement the principle of least privilege by restricting the user's access to a specific subset of resources and data. Account groups are logical collections of cloud accounts, and by associating an administrative user with a particular account group, their access is limited to only those resources and data associated with the cloud accounts within that group. This mechanism ensures that users have access only to the information and resources necessary for their role or tasks, enhancing security by minimizing the potential for unauthorized access or actions within the cloud environment.