A preview variable simulates the results of a view or filter depending on your Perceptive Content environment.
When you run the view or filter without a preview variable, the search results that appear are based on your user name and the current date. However, if the search conditions include the current user or current date variables and you insert preview variables with a different user name or date or both, you can inspect the results as they would appear when viewed by that user, or on the specified date, or both.
Keep in mind that when you run a preview with a user variable, the results appear based on your drawer security. Because the user specified in the preview variable might have access to more drawers or fewer drawers than you, the preview may return more or fewer results for you than it does for the user.