Let's say you have a view whose content can update when it is not in the foreground of its view stack. You need to indicate to the user that your view's content has changed. To do that, use IWorkbenchSiteProgressService#warnOfContentChange().
For instance, in the Eclipse Java Development Tools (JDT), the Problems view can change after each build of a project (the project might gain or add some errors/warnings). If the Problems view is in the foreground of its stack, the change is immediately obvious to the user. If not (let's say you have the Console in front of the Problems view), the view needs to indicate to the user that its content has changed, and it does this by changing its title to bold.