This is a way to stop auto look up facility.
For example when we click on position number field prompt on job data page, it gives all position numbers. But we don't require that but for showing all the values it takes time.
So if we assign that particular prompt table as Lookup Exclusion table then when we click on prompt button for position number it will give a chance to partial search for a value.
navigation to define a record as Lookup Exclusion Table :
PeopleTools --> Utilities --> Administration --> Lookup Exclusion Table.
