When working on large images I am often zoomed in to 400% and only viewing a small portion of the image. This makes it difficult to see any changes in context to the entire image. You could of course zoom in and out to see the overall effect of your changes to the image (the novelty of doing this will soon wear off).
The easy answer is to use the View > New View menu and create yourself a new view of the current image. You can set different parameters for your new view such as the Zoom.
Any changes that you make on either copy of the image will be replicated on the other view. I find that this works great with dual monitors.