Good day.

This article Configure Or Setup Row-Level Security (RLS) In Power BI Using Domain Credentials walks you through setting up Row-Level Security (RLS) on both Power BI Desktop and Power BI Web using Active Directory or Domain credentials specifically using user emails.

As Microsoft mentioned in the documentation, Row-level security with Power BI can be used to restrict data access for given users. Filters restrict data access at the row level, and you can define filters within roles. In the Power BI service, members of a workspace have access to datasets in the workspace. RLS doesn't restrict this data access.

This is useful especially if you belong in a large organization and you want to restrict access of reports to specific people such as top management given that a certain report contains financial and confidential information.