In Travel insights V5 format the column "Mode" specifies if a field is required or optional — all required fields are expected to NOT hold empty or NULL values (e.g. market, currency). Optional fields may be empty (e.g. user device).
"Configuration Groups" are groups of report columns clustered by categories. 'Default' configuration group is always included in the report, meaning that all these columns can't be removed from the report. All other configuration groups (and relevant sets of columns) can be added or removed from the reports, however, column granularity configuration is not supported