Hi Charlie
The “Region of Interest” feature is to allow you to work within a specified ‘region’. Thus, having AE process, only, the pixels within the specified region; resulting in speedier screen previews.
Should you ever want to zoom into an area within the Composition Window, you can do so using the Zoom (Magnifying Glass) tool. Just click towards the top-left of the region/area and then, with the mouse button still depresssed, drag towards the bottom-right of the region/area you would like to zoom into.
Should you ever want to navigate, without affecting any layer within the Composition/Timneline Window, just switch to the Hand Tool, and click and drag as required.
HTH
Best Wishes
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