This policy setting allows you to set the maximum number of the most recently used (MRU) items to display in the Backstage ...

This policy setting allows you to set the maximum number of the most recently used (MRU) items to display in the Backstage navigation pane. 

If you enable this policy setting, you may enter the maximum number of MRU items to display in the pane.

If you disable or do not configure this policy setting, a default of 17 MRU items will be displayed in the pane.