Google recommends using groups for role assignments to streamline access management. By creating groups for each team, adding users to these groups, and assigning roles at the group level, you ensure scalability and ease of maintenance. Providing the Project ID (rather than the Project Number) is preferable because developers typically interact with Google Cloud using the human-readable Project ID in commands and configurations. This approach adheres to best practices by minimizing individual user role assignments and leveraging groups for efficient access control.