Allows you to browse the site as another user (to see what they see) and then quickly switch back again. A general Drupal recommendation is to create test accounts for each of your roles, so this is useful for testing them. (As per notes, don't use it for anonymous access, just log out.) Replacement for 'Switch User'.
Patch and known bug:
- Unmasquerade link appears for users with the permission: 'link to any page', regardless of masquerade status - patch #17 - the bug is as per #22 - Unmasquerade links aren't being shown correctly.