Like other DDCs, Gaffer uses clipping planes in its viewport (the Viewer) for selective rendering. The clipping planes can be set to confine the current view to a selection of scene locations.
To set the clipping plane to enclose one or more locations:
Tip: After the location(s) are selected, you can also hover the cursor over the Viewer and hit Control + K.
To reset the clipping planes back to default: