There is a new trend of fullscreen modals used in web applications. Please refer a sample in the below link (Click the green colored "See it in action" button):
Would like to know the recommended scenarios to use such dialogs?
For instance, if a user previews some content (say an attachment such as image, video, PDF, etc.), then this would be perfect because of the need of larger real estate. On the other hand, if the user has to refer something (say some data) from the underlying screen so as to complete the task, then this won't be recommended.