If you use Filtering, Row Owners, Conditions or User-specific columns then your users will experience your app differently. When designing your app, it's important to be able to preview these different scenarios. For this, we use Preview As.
Below we can see a screen called 'My Tasks'. This list is filtered to only show tasks where the task belongs to the person who is logged in. Initially this screen is empty, but as we use Preview as with different emails we can see the list changes to display what that user would see.