We hear this a lot from users: you used to be able to edit or view a page full-screen. Ever since we've introduced Magnolia 5, this is no longer possible. The use cases for full-screen editing and preview are:

• you may edit a page without any chrome around it. No distraction, just you, the page and some actions.
• you may view a page in its actual size while previewing it. If you resize the browser window, the page adjusts.
• while developing page templates, again, this is a way to also verify if a page properly handles different page widths and heights.
• direct access to a full-screen edit view of a page was sometimes the only access a customer would give to a select set of editors. If you're responsible for your department's main page and a couple of sub pages that could be reached from there, you'd get a link to the edit view of that page. No need to teach you all the backend. There's no simpler UI than that.