By default, the "Single line mode" option is selected (ticked). The details for each of the documents in the list will display in a single line. If you select this option, a column header "Use your mouse to pull a column here to group on that column" will be not be displayed on which the similar data in columns can be grouped.

Single line mode selected

The details for each of the documents in the list will display in a single line.

Single line mode not selected

If the  "Single line mode" option is not selected a column header "Use your mouse to pull a column here to group on that column" will be displayed and the similar data in columns will be grouped.

All similar data in columns will be displayed once, e.g. Dates, Document groups, Salespersons, etc.