This option will only appear when working with OLAP, Tabular, and BW hierarchies or 'Regular' hierarchies.' It allows users to 'expand down' on multiple hierarchies and hierarchy levels in the query. By default, expand icons are enabled, so that grids containing regular hierarchies will display the expand and collapse icons.
Toggle the Expand Icons button on or off from the Component ribbon. In the example below, expand icons are enabled. The grid contains 2 regular hierarchies, 1 on rows and 1 on columns. Each row and column header cell displays the relevant expand or collapse icon (excluding those cells containing member elements from the lowest level of the hierarchy).
Expand icons can also be shown via the Matrix Grid view of the Formatting Panel (red highlight below):
Here, expand icons are disabled. Because some elements were expanded when the icons were disabled, these levels remain exposed in the grid.
Open the Expand Icons drop down to enable the expand icons for rows or columns only. Here, they are enabled only for rows.