Some applications can change their user interface in response to changes in their settings (i.e. changes triggered by the real-time framework, especially through the PCP), while others require a restart before the new settings get applied. Some applications can do this for some settings but not for others. For example, on Windows 7, only "high contrast" can be modified live, whereas on Fedora 20 with GNOME, all magnifier settings (mag-factor, mouse-tracking, screen position), font size, cursor size, gtk-theme & icon theme (both for high contrast) can respond live.
Having this information in a machine-readable way would allow the PCP (or any other user interface provided by GPII) to let the user know which changes to the settings can be applied live and which require a restart of an application.