Relating workbooks gives users access to workbooks they previously did not have access to. It's a great workaround to give users partial access to a workbook but you should be careful with what data you expose.
Who can relate rows
Users with the Manager or higher permission to both the linking and linked worksheets can set up related rows. Users with Editor or higher permissions cannot link worksheets but can choose rows to relate, edit related rows, and add new rows when worksheets are already linked.
Note: Relating a row gives users view or write access to all data in that row.
Using related rows as a form of access control
With the right related row setup, you can allow users without direct access to your workbook to edit that workbook. For instance, if you have a workbook of job openings that you want to share with team members to have their help in editing the job description, you can relate rows to your HR tracking workbook. But make sure you don't relate rows with data you'd prefer to keep hidden.
Wrong way to relate rows for access control
For instance, in the animation below, we have a new workbook for showing job openings without their salary details. But we related rows with the full details. So even though we didn't include related row lookups with the salary, users can still expand the row and get the salary details!
Better way to relate rows for access control
In the animation below, we fix this problem. We have one worksheet for shareable data (Job Openings) and another worksheet for hidden data (2022 Hiring Budget) where we have moved our hidden data (salary) to, but still referencing our shareable worksheet (for the job details). This time, when users expand our related rows in the lookup workbook, they can't see our hidden information.
See our article on Workbook sharing and permissions for more detail on user permissions.