Respect user choice
Let the user decide, if possible, whether to open your application on Workbench or on another screen. If he decides to open it on a custom public screen, let him choose whether it will be a new screen or one that has already been created by a different application.
Likewise, respect choices the user has already made. All custom screens, whether public or private, should default to the basic parameters established in Workbench's Preferences, unless your application has special requirements.
If your application provides overscan capabilities you should respect the settings that the user has established in the Overscan editor found in Workbench's Prefs directory.