Thanks everyone for your responses, "would a rose by any other name......." the name of the zoom slider contained in the navigator tab is immaterial - using the slider causes magnification. If you magnify a page, so only part of the page is visible, you can then 'navigate' by moving the "grey box". I think a better use of the navigator panel would be the ability for the user to be able to add "jump to places" within a document. A bit like word search, the ability to define your own 'jump to places'. which the user could name. Using a + or - icon could add or remove the" jump to" points. These points (and you could have dozens) would then be shown in the navigator panel. Of course if it was really clever when you select the magnifying tool on the tool bar the 'navigator panel' could change its content to reveal the "grey box navigation/magnification facility" that it currently has. Move off the magnifying glass should cause the navigator panel to revert to showing your 'jump to' places.
While this is partly done in the "layers" panel, it would be better if you could create your own "jump to point" within the same or varying layers. If you have a document with a hundred plus pages and a large number of layers the ability to navigate quickly to a specific point, be it picture or an individual word in the document would be useful.
As the same slider exists in Photo it would be useful (when in photo) to use it to define different areas of a picture for example if you had a photo of Snow White and her seven dwarfs and wanted to edit each dwarfs face - creating a magnified "jump to" for each face would save time. I appreciate using the magnifying glass and centering it over the required spot effectively does the same thing but again I consider that to be magnification not 'navigation'.