To open a particular type of file, such as a music file, an image or a web page, Windows uses a default program. In this dialog, a specific program can be set as default for a specific file type.
The Default Programs feature applies only when the package is installed on Windows Vista or later. For lower systems, it's ignored.
Register application with Default Programs
This option enables you to register an application from your package to be used through Windows Default Programs (Vista or above).
For additional information please, see Microsoft's Platform SDK documentation.
This section allows you to specify all the information needed to register an application to Windows Default Programs.
Set your defaults
This section allows you to specify what files types should be associated by default with the application you registered in Windows Default Programs.
This is achieved with the use of a custom action which is running at the end of the installation.
The options you set here only apply to the user that performs the installation. Your choices won't affect other user accounts on the machine. Also, all the settings performed after the installation through the Default Programs UI will apply only to the current user.