This seems like a no-brainer... to be able to toggle between any zoomed position and Fit View while editing. Often I'm zoomed in while working on refining a mask and need to view the full image, then toggle back again. But there's no shortcut key for Fit view. You have to click on "Fit" in the Navigator or Hit Cmd - several times. Although it zooms out, it doesn't go to Fit view. You should be able to press the number "0" to always return to Fit view.