gsksun4 - It allows you to maximize the viewport. This gives you a model space view while working in a viewport. The advantage of working in this mode is the ability to work in model space with all the layers frozen in the viewport. You can double click outside the "red rope" to minimize the view.
Just curious, why don't you scale and lock your viewport while you are inside the viewport?
Select the scale from the viewport scale list on the status bar and then click on the padlock.