Switch User allows you to temporarily assume the identity of another user.
You can use it for many cases, such as:
reproducing and troubleshooting problems specific to a user to diagnose permissions issues.
updating an issue on behalf of another user if they are unavailable.
and many other issues and cases
To switch back to the original user, click the icon in the top right corner of the menu bar
When is used, it will generate a log entry in the audit log like so: