This optional setting appears under VPS: Lister Settings. It is specific to ProcessWire's Lister and applies to Modal Lister view.
Use the setting to specify the default columns to show in the Lister. If the setting is left empty, the default Lister columns (title, template, etc.) will be displayed. If you use the setting, please note that the column Title will always be required. It is needed to enable selection of pages to add to the page field. The Columns Tab in the Lister will be displayed.