This policy setting controls the "Tell me if Microsoft Excel isn't the default progam for viewing and editing spreadsheets" ...

This policy setting controls the "Tell me if Microsoft Excel isn't the default progam for viewing and editing spreadsheets" option found under File tab | Options.If you enable or do not configure this policy setting, Excel will show an alert if it isn't the default progam for viewing and editing spreadsheets. This is the default behavior.If you disable this policy setting, Excel will turn off the alert.