Your company has a team of 50 data scientists who all need the 'BigQuery Data Viewer' role on a specific project. Team members frequently join and leave the company.

What is the MOST efficient and secure way to manage these IAM assignments?

The best practice for managing IAM roles for multiple users who share the same job function is to use Google Groups. You create a group (e.g., data-scientists@company.com), add the users to the group, and then assign the necessary IAM roles to the group itself. When a new person joins, you simply add them to the group, and they automatically inherit the permissions. This drastically reduces administrative overhead and prevents orphaned permissions when people leave.