When viewing Rialto in the split view, this allows you to control the width of the two panes that are displayed. This is especially useful for people who prefer to not use the mouse. Once you select this button, three more buttons appear. Select the desired button to set the desired pane width. For example, if you select the left button, the offers list takes up less space than the details pane:

Users who use the mouse can control the panes width by dragging the divider between the two panes to the right or left.

The list of offers is displayed alongside the details of the selected offer. 

This view is particularly suited for users who work on machines with screens smaller than 1024px (such as laptops, iPads, etc.). This view displays the most important information you need to get your job done, while hiding the less important information.

• The details pane of the offer takes up the screen, and the list of offers becomes hidden. If you have several offers in your lists, navigate between them using the Up and Down arrows. To display the list, select Back to List on top of the page. 
• The left panel is collapsed by default (you can open it, if needed). If you have opened it, it will close again when you navigate to a different offer. 
• The facets list becomes hidden.  
• The header disappears.