Some time ago, Facebook introduced a feature that helps set up the permissions on ones profile: view as someone else. It allows the author of a dynamic page to see which user groups (or specific users) can see which information in the page, and thereby debug the permissions. A similar feature exists in LinkedIn
The modern applications, especially B2B, may have much more complex permission settings. Therefore such tool is much more useful. However as far as I know, this function is not very wide spread. I wonder what the disadvantages may be, or if there is any RFC and best practice article I can read before considering it for my own project.