If you check allow drilldown for a transform, double-clicking a cell in the Right pane data table shows the rows in the upstream dataset that this cell/row was derived from. For example you can double-click a cell in a pivot table to drilldown into the rows it was calculated from:
The following transforms allow drilldown:
Note that enabling drilldown slows down processing and requires more memory.
See also:
•Video: How to drilldown into data